Objective lens system for endoscopes

ABSTRACT

An objective lens system for endoscopes comprising, in the order from the object side, a first lens unit having negative refractive power and a second lens unit having positive refractive power, said first lens unit comprising a surface which is concave on the image side and satisfies the following condition (1), and an aspherical surface which is arranged on the object side and satisfies the following condition (2) at 50% or more of the effective area thereof. ##EQU1##

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an objective lens system for endoscopeshaving favorably corrected aberrations, especially distortion.

(b) Description of the Prior Art

As one of the conventional objective lens systems for endoscopes, thereis known the retrofocus type of lens system illustrated in FIG. 1.

The retrofocus type objective lens system for endoscopes comprises alens unit L₁ having negative refractive power on the object side of anaperture stop S and a lens unit L₂ having total positive refractivepower on the image side of the aperture stop. The lens unit L₁ has thenegative refractive power for widening field angle of the objective lenssystem and the lens unit L₂ has an imaging function, thereby composing atelecentric optical system having the characteristics of the objectivelens system for endoscopes to have a large visual field angle and toallow the principal ray P to be perpendicularly incident on the imagesurface regardless of image height.

The reason for the objective lens system for endoscopes to have thetelecentric characteristics is that the angle of incidence is limitedfor the rays capable of falling on the end surface of an image guidecomposed of an optical fiber bundle, a solid-state image pickup devicesuch as CCD or a relay lens system having entrance pupil thereof locatedat infinite distance when such a member is arranged on the image surfaceof the objective lens system. In other words, transmission efficiency islowered and images are darkened when the principal ray emerging from theobjective lens system falls obliquely on the image surface.

Further, the objective lens system for endoscopes having theabove-described composition can easily be assembled and manufactured ata low cost though the lens system has a small diameter of severalmillimeter since the outside diameters of the lens units L₁ and L₂ arenearly equal to that of the image guide though the lens system has alarge field angle, and the lens system is compact and comprises a smallnumber of lens elements.

Illustrated in FIG. 2 is another conventional example of objective lenssystem for endoscopes disclosed by Japanese Unexamined Published PatentApplication No. 226315/59.

This retrofocus type objective lens system for endoscopes comprises alens unit L₁ ' having negative refractive power on the object side of apupil position S and a lens unit L₂ ' on the image side of the pupilposition S, and has a composition similar to that of the objective lenssystem shown in FIG. 1. Though the pupil is located with the lens unitL₂ ', no inconvenience is caused by making discussion on an assumptionthat the lens unit L₂ ' is located as a whole on the image side of thepupil S since the lens unit L₂ " arranged on the extremely object sidein the lens unit L₂ ' is composed of a plano-convex lens componenthaving a plane surface on the side of incidence. However, the objectivelens system shown in FIG. 2 uses, in the vicinity of the pupil S, abar-shaped lens component L₂ " which is longer in the direction alongthe optical axis than the diameter thereof.

Endoscopes are classified into flexible endoscopes which can be flexedfreely and non-flexible endoscopes which cannot be flexed. The flexibleendoscopes permit freely changing direction of visual field forobservation, whereas the non-flexible endoscopes allows observation onlyin a certain definite direction and the forward viewing objective lenssystem shown in FIG. 1 permits observing objects located only in thefront direction. Therefore, side viewing, oblique viewing and backwardviewing objective lens systems are separately necessary to observeobjects located in different directions through the non-flexibleendoscopes.

In contrast, the objective lens system shown in FIG. 2 enables toobserve objects located in different directions by using, in thebar-shaped lens component L₂ ", various types of field directionchanging prisms such as shown in FIG. 3A, FIG. 3B and FIG. 3C.

In the objective lens system shown in FIG. 2, it is practicallydifficult to arrange an aperture stop having a light-shielding functionat the pupil position S since it is to be located in the lens componentL₂ '.

FIG. 4 shows an optical system which is composed of the objective lenssystem shown in FIG. 2 combined with relay lens systems. In this opticalsystem, an image of an object O₁ formed by the objective lens system istransmitted sequentially as O₂, O₃ and O₄ through relay lens systems R₁,R₂, R₃, . . . , and position of the pupil determining brightness is alsotransmitted simultaneously. Though S corresponds to the pupil positionin the objective lens system, S₁, S₂ and S₃ correspond to pupilpositions in the relay lens systems, and diameter of the relay lenssystems is equal to that of the pupils S₁, S₂ and S₃ in most cases. Forthis reason, brightness of optical system is determined almost byoutside diameter of the relay lens systems and it is not alwaysnecessary to arrange an aperture stops having the light-shielding effectat the pupil position S of the objective lens system.

When inclination angle relative to the optical axis θ of the principalray P incident on the lens unit L₁ (L₁ ') located on the object side ofthe aperture stop is compared with inclination angle relative to theoptical axis θ' of the principal ray P emerging from the lens unit L₁(L₁ ') and incident on the lens unit L₂ (L₂ ') arranged on the imageside of the aperture stop in the objective lens systems shown in FIG. 1and FIG. 2, θ' is far smaller than θ. This is because the lens unit L₁has negative refractive function for widening the visual field angle.

In such objective lens systems, there is established the followingrelationship between the small angle θ' and aberrations. Speakingconcretely, curvature of field, astigmatism and distortion are producedin small quantities in Seidel's aberrations, whereas sphericalaberration and coma are produced in relatively large quantities. Thisrelationship is visualized in FIG. 6. Accordingly, it is sufficient todesign the lens unit L₂ having positive refractive power in such amanner that it forms an image having spherical aberration and comacorrected on an assumption that the pupil S located between the lensunit L₁ and the lens unit L₂ is an object. The sine condition is knownas the requirement for designing a lens unit for forming such an image.When image height is represented by I, focal length of the lens unit L₂is designated by f₂ and the inclination angle relative to the opticalaxis of the principal ray P is denoted θ', the sine condition for thetelecentric optical system wherein the principal ray P is incidentperpendicularly on the image surface I can be expressed by the followingformula:

    I=f.sub.2 sin θ'

Further, for the lens unit L₁, the sine condition is satisfied to acertain degree also on the front side of the aperture stop when the lensunit L₁ is composed of a single spherical lens element as shown in FIG.7. Accordingly we obtain the following relationship:

    I=f sin θ

wherein the reference symbol f represents focal length of the objectivelens system as a whole and the reference symbol θ designates inclinationangle relative to the optical axis of the principal ray P incident onthe lens unit L₁.

Almost all the objective lens system for endoscopes which are usedcurrently satisfy the abovementioned sine condition since the lenssystems have small outside diameters and comprise small numbers of lenselements.

When the above-mentioned sine condition is satisfied, distortion isaggravated abruptly as field angle θ is enlarged as shown in FIG. 6.Relationship between distortion and field angle θ can be expressed bythe following formula:

    DT(θ)=(cos θ-1)×100 (%)

wherein the reference symbol DT represents distortion which is given bythe following formula: ##EQU2## wherein the reference symbol yrepresents size of an image deformed by distortion and the referencesymbol y₀ designates size of an ideal image calculated by the paraxialtheory.

When the sine condition is satisfied and distortion has theabove-mentioned relationship with the inclination angle θ, negativedistortion (barrel-shaped distortion) is aggravated abruptly as theinclination angle θ is enlarged.

The conventional objective lens system for endoscopes shown in FIG. 2,for example, has the following sine condition:

    I=0.91

    f sin θ=1.27×sin 45°=0.898

Further, the above-mentioned objective lens system for endoscopes hasdistortion expressed below:

    DT (ω.sub.1 =45°)=-30%

    (cos 45°-1)×100 =-29.3%

Further, in an objective lens system almost satisfying the sinecondition of I=f sin θ (hereinafter referred to as an objective lenssystem of I=f sin θ type), DT(θ) has the values listed below at variousvalues of θ:

    ______________________________________                                        Field angle (2θ)                                                                    40°                                                                           60°                                                                            80°                                                                         100°                                                                        120°                                                                        140°                         Distortion (DT(θ))                                                                  -6     -13.5   -23  -36  -50  -66 (%)                             ______________________________________                                    

FIG. 8 and FIG. 9 exemplify how images affected by distortion actuallylook like. FIG. 9 visualized images of the lattice patterns arrangedvertically and horizontally at equal intervals on a plane perpendicularto the optical axis shown in FIG. 8 which are formed by using objectivelens systems having DT's of 0% to 30% at the maximum image height.

As is understood from the foregoing description, the conventionalobjective lens systems have remarkable negative distortion though thelens systems have wide field angles which are indispensable for theseobjective lens systems for endoscopes, are designed as telecentric lenssystems, and satisfy the requirements of favorably corrected aberrationsand compact design.

The objective lens systems for endoscopes having distortion form imagesof marginal portions of an object which are smaller and more distortedthan the images of central portions. Accordingly, it is impossible tomeasure or analyze shapes accurately by applying the objective lenssystem having distortion to inspection of industrial products, orerroneous diagnoses may be made by using such objective lens system inthe field of medicine.

Further, in a wide-angle photographic lens system having littledistortion and a wide angle as shown in FIG. 10, for example, thefollowing relationship establishes:

    I=f tan θ

In an objective lens system satisfying the abovementioned relationship,light quantity reduces on the image surface thereof at a rate of cos⁴ θas θ has larger values. In the conventional objective lens system forendoscopes having the remarkable negative distortion, on the other hand,images of the marginal portions are smaller than those of the centralportions when portions of the same size over the entire range from thecenter to the marginal areas are observed, and the reduction of theimage size cancels the reduction of light quantity at the rate of cos⁴θ. Accordingly, in the objective lens systems satisfying therelationship of I=f sin θ, brightness is not reduced as inclinationangle θ is enlarged but uniform over the entire range from the center tothe marginal areas. In other words, the objective lens systems forendoscopes satisfying the sine condition have the above-described defectdue to the distortion though such lens system can provide uniformbrightness.

Furthermore, it is possible to compose oblique viewing, side viewing andbackward viewing objective lens systems for endoscopes by combining theobjective lens systems for endoscopes with the field direction changingprisms shown in FIG. 3A, FIG. 3B and FIG. 3C as already described.

When the field direction changing prisms are arranged at positionsslightly deviated, however, these prisms adversely affect images formedby the objective lens systems.

A field direction changing optical system for oblique viewing isexemplified in FIG. 11 wherein a correcting prism 2 is arranged before afield direction changing prism 1 for correcting astigmatism. Inaddition, the negative lens unit L₁ is arranged on the object side ofthe correcting prism 2.

In this field direction changing optical system, the center of the lightbundle emerging from the exit surface 1a of the prism 1 shown in FIG. 11is deviated from the optical axis of the lens unit L₂ due to deviationof arrangement location of the prism caused at the stage of assemblyand/or manufacturing error of the prism shape. When the center of theemerging light bundle is deviated from the optical axis of the lens unitL₂ as described above, the light l which is to travel in alignment withthe optical axis of the lens unit L₂ is incident on the lens unit L₁ atan angle of θ relative to the optical axis of the lens unit L₁, therebydegrading image quality. Further, image quality is degraded also whenthe prism 1 is arranged in a position inclined relative to the lens unitL₂.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide an objectivelens system for endoscopes having a large field angle and distortionsufficiently corrected, and forming images whose brightness is uniformover the entire range from the center thereof to the marginal portionsthereof.

Another object of the present invention is to provide an objective lenssystem for endoscopes comprising a field direction changing opticalsystem arranged between the lens units composing the objective lenssystem.

A third object of the present invention is to provide an objective lenssystem having such a composition as to facilitate to arrange the fielddirection changing optical system with little eccentricity relative tothe optical axis.

The objective lens system for endoscopes according to the presentinvention has the composition illustrated, for example, in FIG. 3,comprises, in the order from the object side, a first lens unit L₁ whichcomprises a negative lens component having a concave surface on theimage side and has negative refractive power, and a second lens unit L₂which has positive refractive power, and is so designed in such a mannerthat the image side surface of said negative lens component satisfiesthe following condition (1):

    |R.sub.1 |≦3f                     (1)

wherein the reference symbol f represents focal length of the objectivelens system as a whole and the reference symbol R₁ designates radius ofcurvature on said concave surface.

If |R₁ | has a value large enough to exceed the range defined by thecondition (1), it will be necessary to increase the number of thesurfaces having negative refractive powers in the first lens unit L₁ forobtaining a large visual field, thereby enlarging outside diameter ofthe objective lens system. When the objective lens system has such alarge diameter, the lens machining and assembly works for arranging thelens units within a space having an outside diameter of at most severalmillimeters of endoscopes will become tedious, thereby enhancingmanufacturing cost of the objective lens system. Further, it will beimpossible to obtain performance of the objective lens system sufficientfor practical use due to variations of individual component memberswhich are used in an increased number and to reserve a space forarranging the field direction changing prism, thereby making theobjective lens system unsuited for use with endoscopes.

Further, the objective lens system for endoscopes according to thepresent invention comprises, as at least one of the object side surfacesof the first lens unit L₁, at least one aspherical surface satisfyingthe following condition (2) at 50% or more of the effective area of thelens surface determined by the light bundle having the maximum imageheight, i.e., the area of the lens surface indicated by ES in FIG. 17:##EQU3## wherein the reference symbols ω_(I) and ω₀.5 represent fieldangles at an image height of I and 1/2 of the maximum image heightrespectively, the reference symbol K_(I) designates, when K is definedas K=sin θ₂ /tan θ₁, value of K at the image height I, the referencesymbol K₀.5 denotes value of K at 1/2 of the maximum image height, thereference symbol θ₁ represents angle formed between the optical axis andthe principal ray incident from the object side on the asphericalsurface arranged on the extremely object side, and the reference symbolθ₂ designates angle formed between the optical axis and the principalray immediately after said ray is refracted by the aspherical surfacelocated on the extremely image side.

When the objective lens system for endoscopes according to the presentinvention comprises only one aspherical surface, however, the referencesymbol θ₁ represents angle formed between the optical axis and theprincipal ray incident on said aspherical surface, and the referencesymbol θ₂ designates angle formed between the optical axis and theprincipal ray refracted by said aspherical surface.

In order to accomplish the above-mentioned objects, the objective lenssystem according to the present invention is so designed as to satisfythe following formulae (i) and (ii) in FIG. 13:

    I=f.sub.2 sin θ.sub.3                                (i)

    I=f tan θ.sub.1                                      (ii)

wherein the reference symbol f represents focal length of the objectivelens system as a whole, the reference symbol ef₂ designates total focallength of the second lens unit L₂ and the reference symbol θ₃ denotesangle formed between the optical axis and the principal ray incident onthe second lens unit L₂.

The formula (i) is a condition necessary for favorably correctingspherical aberration, coma and so on, and satisfied by a lens systemwherein the second lens unit L₂ has positive refractive power. Whenangle θ₃ is enlarged in the second lens unit L₂, distortion is producedbut poses no problem since the angle θ₃ is small. Further, the lenssystem satisfying the formula (i) can provide uniform brightness overthe entire range from the center to marginal portions of an imageregardless of enlargement of the angle θ₃. The formula (ii) is satisfiedby an optical system free from distortion. Accordingly, the objectivelens system for endoscopes according to the present invention is sodesigned, unlike the conventional objective lens systems satisfying I=fsin θ₁, as to correct distortion and provide an image having uniformbrightness over the entire range from the center to the marginalportions thereof by modifying composition of the optical system in sucha manner that I=f tan θ₁ for the objective lens system as a whole issatisfied by the first lens unit L₁ while satisfying the sine conditionfor the second lens unit L₂.

In case of a lens system for which outside diameter thereof and numberof lens components therein are limited like an objective lens system forendoscopes, it is necessary to use at least one aspherical surface formodifying the first lens unit L₁ as described above.

Now, description will be made on the aspherical surface to be used forthis purpose.

When attention is paid to the principal ray P at an optional imageheight in FIG. 13, I and θ₁ must satisfy the formula (ii) on the objectside of the aspherical surface ASP. For I and θ₂ of the principal rayimmediately after emerging from the aspherical surface ASP, on the otherhand, the following formula (iii) establishes since the second lens unitL₂ satisfies the sine condition:

    I∝f sin θ.sub.2                               (iii)

In order to correct distortion not only at an optional image height butalso over the entire range from the center to the marginal portions ofan image, the above-mentioned formulae (i) and (iii) must establish forthe rays at all the image heights. From the formulae (i) and (iii), thefollowing formula (iv) can be obtained: ##EQU4##

That is to say, K must be constant in the formula (iv) for correctingdistortion at all the image heights.

Let us assume here that K varies in the formula (iv). Relationshipbetween the principal ray and the aspherical surface ASP is visualizedin FIG. 14A and FIG. 14B. In these drawings, the angle θ₂ is equal onboth the aspherical surface having a large value of K shown in FIG. 14Aand the aspherical surface having a small value of K shown in FIG. 14B.

When the principal ray P is assumed to be at an optional image height inFIG. 14A and FIG. 14B respectively, positive distortion is produced bythe principal ray travelling to the area at which value of K is enlargedfrom the center of an image toward the marginal portion thereof. Incontrast, negative distortion is produced by the principal ray to thearea at which value of K becomes smaller from the center of an imagetoward the marginal portion thereof. That is to say, positive distortionis produced at the area at which value of K increases toward themarginal portion of an image, whereas negative distortion is produced atthe area at which value of K decrease toward the marginal portion of animage. Relationship between value of K and nature of distortion producedat that value of K is summarized as the following (a) through (d):

    K.sub.0 >K.sub.0.5 >K.sub.1                                (a)

    K.sub.0 <K.sub.0.5 <K.sub.1                                (b)

    K.sub.0 <K.sub.0.5 >K.sub.1                                (c)

    K.sub.0 >K.sub.0.5 <K.sub.1                                (d)

wherein the reference symbol K₀ represents value of K at a location ofimage height 0, the reference symbol K₀.5 designates value of K atlocation of 1/2 of the maximum image height and the reference symbol K₁denotes value of K at a location of the maximum image height.

When K₀, K₀.5 and K₁ are in the relationship summarized in (a) through(d) above, images look like as illustrated in FIG. 15A, FIG. 15B, FIG.15C and FIG. 15D respectively.

In most cases where objects are observed through endoscopes, thesurfaces thereof are rarely planes perfectly, but are mostly concave,convex or tubular. Therefore, it is not always necessary that value of Kis constant over the entire range from the center of an image tomarginal portion thereof, and variations as summarized in (a) through(d) may be desirable for practical use.

When the conventional objective lens system for endoscopes is consideredas illustrated in FIG. 13, the following formulae (v) and (vi)establish:

    I=f sin θ.sub.1                                      (v)

    I=f.sub.2 sin θ.sub.3                                (vi)

On the other hand, the following formulae (vii) and (i) establish for anoptical system having aberrations corrected at all image heights:

    I=f tan θ.sub.1                                      (vii)

    I=f.sub.2 sin θ.sub.2                                (i)

In the similar way as that described above, it is possible to express K'as K'=sin θ₃ /sin θ₁ from the formulae (v) and (vi), and K as K=sin θ₃/tan θ₁. Since K and K' can be expressed in the same form of f₁ /f₂, itis possible to express difference between K' of the conventional opticalsystem and K of an optical system having corrected aberrations in thefollowing form of a ratio between K' and K:

    K'/K=sin θ.sub.1 /tan θ.sub.1 =cos θ.sub.1

This means that value of K varies at a rate of cos θ₁ in theconventional objective lens systems for endoscopes. When value of K atthe center of an image is represented by K₀, it is therefore possible toexpress the value of K at a field angle of θ₁ as follows:

    K.sub.0 ×cosθ.sub.1                            (viii)

Accordingly, in order to reduce distortion over the range from thecenter of image to the marginal portion thereof, for example, it isnecessary that difference Δk₀₋₁ in value of K between the center of animage and the marginal portion thereof satisfies the followingrelationship:

    ΔK.sub.0-1 <K.sub.0 (1-cos ω.sub.1)

wherein the reference symbol ω₁ represents field angle at the maximumimage height.

However, the objective lens system satisfying the sine condition tendsto aggravate distortion abruptly toward the marginal portion of an imageas is seen from FIG. 9 and the aberration characteristics (FIG. 51) ofthe conventional optical system illustrated in FIG. 4. Accordingly,deformation of an image due to distortion is sufficiently little withinthe range up to 1/2 of the maximum image height. It is thereforesufficient to select the range from 1/2 of the maximum image height tothe marginal portion of an image as the range for correcting distortion,and correction of distortion is important within this range.

In view the fact described above, it is sufficient to satisfy theabove-mentioned condition (2) for correcting distortion sufficientlyfavorably. If the condition (2) is not satisfied, distortion will beproduced, thereby making the objective lens system for endoscopesunsuited for industrial or medical use.

For the aspherical surface adopted for satisfying the condition (2), itis sufficient to satisfy the condition (2) at least 50% of the effectivesurface area determined depending on the light bundle having the maximumimage height. When the condition (2) is satisfied at an effectivesurface area less than 50%, the objective lens system will beundesirable because distortion is corrected only at narrow area.

When the maximum image height is represented by I_(max) and height ofprincipal ray on the first surface to attain to the maximum image heightis designated by h₁ in the objective lens system for endoscopesaccording to the present invention, it is desirable to design the lenssystem so as to satisfy the following condition (3):

    h.sub.1 /I.sub.max ≦2                               (3)

FIG. 16 shows a sectional view of the objective lens system forendoscopes according to the present invention which is to be used in anon-flexible endoscope and comprises an oblique viewing prism. In thisdrawing, the reference symbol C represents a cover glass, and thenon-flexible endoscope contains an objective lens system which comprisesa first lens unit L₁ consisting of a negative meniscus cemented doublet,and a second lens unit L₂ consisting of a positive lens component 5serving also as a field direction changing prism, cemented doublet 6 anda meniscus cemented doublet 7. The first lens unit L₁ is cemented to thesurface of incidence of the positive lens component 5, whereas thepositive lens component 6 is cemented on the side surface thereof to thetip of an inner tube 10. The positive lens component 1 and the cementeddoublet 6 are positioned relatively to each other with a spacing ring 8,whereas the cemented doublet 6 and the meniscus cemented doublet 7 arepositioned relatively to each other with a spacing ring 9. Further, thespacing ring 9 has an edge 9a which extends inward and serves as a flarestop. The reference symbol LG represents a light guide. The endoscope isrestricted in the outside diameter thereof and, on the other hand, mustallow the cover glass to reserve a margin for the rays to passtherethrough. If the cover glass has no margin, light quantity will beinsufficient at marginal portions of an image and the image will beaffected by detrimental rays.

In view of this point, the condition (3) defines relationship betweenthe maximum image height and the first surface of the objective lenssystem for endoscopes. If the condition (3) is not satisfied, a smallvalue of I_(max) for a large value of h: will make an image too smallfor favorable observation. Further, field angle will be narrowedundesirably for the objective lens system for endoscopes which shouldpreferably have a wide angle.

When focal length of the second lens unit L₂ is designated by f₂, andthe surface having the smallest radius of curvature out of the surfaceswhich are concave on the image side and arranged in the first lens unitis represented by R_(min), it is desirable to design the objective lenssystem for endoscopes according to the present invention so as tosatisfy the following condition (4) and (5):

    f≦f.sub.2 ≦10f                               (4)

    |R.sub.min |≦1.5f                 (5)

In the objective lens system for endoscopes, the formula (i) establishesfor focal length of the second lens unit L₂. If f₂ is smaller than thelower limit of the condition (4) in this objective lens system, θ₂ willbe large so long as value of I is constant. When it is necessary toreserve a space for arranging the field direction changing prism betweenthe first lens unit L₁ and the second lens unit L₂ as shown in FIG. 13,the angle formed between the optical axis and the off axial ray is largein this space, thereby undesirably making it difficult to satisfy thecondition (3). If f₂ is larger than the upper limit of the condition(4), in contrast, θ₂ will be small at a constant value of I. When it isattempted to enlarge the field angle of the objective lens system as awhole, it will be obliged to strengthen the negative refractive power ofthe first lens unit L₁, and correction of aberrations and adjustment ofeccentricity at the assembly stage will undesirably be difficult.

When focal length f₂ of the second lens unit L₂ is set within the rangedefined by the condition (4), it is necessary to relatively strengthenthe negative refractive power of the first lens unit L₁ for widening thefield angle. In the composition illustrated in FIG. 4, however, it isdifficult to arrange a plural number of lens components having negativerefractive powers in the first lens unit L₁. Accordingly, it isnecessary for widening the field angle to design the concave surfacehaving negative refractive power in the first lens unit L₁ so as tosatisfy the condition (5). If the condition (5) is not satisfied, itwill be difficult to widen the field angle.

It is possible to design the objective lens system for endoscopessatisfying the conditions (4) and (5) so as to be separable in thevicinity of the pupil position between the first lens unit L₁ and thesecond lens unit L₂, and selectively use plural numbers of differentfirst lens units and second lens units having various refractive powersand viewing directions in accordance with purposes of practicalapplication.

When the aspherical surface satisfying the condition (2) to be used onthe first lens unit L₁ of the objective lens system for endoscopesaccording to the present invention is a surface located on the objectside, it is more desirable to design the aspherical surface so as tohave a shape satisfying the following condition (6);

    0≦ tan α ≦ tan ω.sub.1           ( 6)

wherein the reference symbol o represents angle formed between theaspherical surface and the plane perpendicular to the optical axis atthe intersection between the principal ray having the maximum imageheight I_(max) and said aspherical surface. In addition, sign of α isregarded as positive when the aspherical surface is inclined on theimage side as illustrated in FIG. 17.

In FIG. 17, Snell's law allows the following formula to establish forthe ray incident on the above-mentioned intersection:

    sin (θ.sub.1 -α)=n sin (θ.sub.2 -α)

Wherein the reference symbol n represents refractive index of theaspherical lens on an assumption that air is located on the object sideof the aspherical surface.

The above-mentioned formula can be developed as follows:

    sin θ.sub.1 -cos θ.sub.1 tan α=n sin θ.sub.2 -n cos θ.sub.2 tan α                                 (ix)

In the above formula (ix), tan α represents angle formed between theaspherical surface and the plane perpendicular to the optical axis atthe above-mentioned intersection, and the following formula (x) can beobtained from the above-mentioned formula (ix):

    tan α= (n sin θ.sub.2 -sin θ.sub.1)/(n cos θ.sub.2 -cos θ.sub.1)                                       (x)

Further, the formula (iv) k=sin θ₂ /tan θ₁ gives the followingrelations: ##EQU5##

By using these relations in the formula (x), we obtain: ##EQU6##

As is seen from the formula (xi), tan α is enlarged as K has a largervalue. That is to say, the aspherical surface is inclined on the imageside at a larger angle as K has a larger value, and vice versa. Further,when tan α is zero, the aspherical surface is perpendicular to theoptical axis at the above-mentioned intersection and the asphericalsurface having K_(I) -K₀.5 satisfying the condition (2) at this time hasthe shape shown in FIG. 18A. Furthermore, at tan α<0, the asphericalsurface has such a shape as to be concave on the object side at highercarvature as the surface portions are closer to the optical axis, whichis undesirable since such a surface maKes it difficult to correctaberrations.

Moreover, at tan α=tan ω₁, the principal ray is incident perpendicularlyon the aspherical surface at the above-mentioned intersection andtravels straight without being refracted by the aspherical surface. WhenK_(I) -K₀.5 satisfies the condition (2) at this time, the asphericalsurface is shaped as shown in FIG. 18B. At tan α=tan ω₁, the asphericalsurface has such a shape as to be convex on the object side at highercurvature as the surface portions are farther from the optical axis,thereby maKing it difficult to enlarge the field angle. Since the rayrefracted by this aspherical surface has a large angle relative to theoptical axis and the ray incident on the second lens unit L₂ has asufficiently small angle relative to the optical axis, the negativefunction of the first lens unit L₁ is strengthened. Accordingly, thesurface concave on the image side on the first lens unit L₁ hascurvature of smaller absolute value and the number of the lenscomponents having negative refractive powers in the first lens unit L₁must be increased, thereby producing undesirable effects on correctionof aberrations and assembly worKs of the objective lens system.

Accordingly, it is desirable that tan α satisfies the condition (6).

When shape of the aspherical surface satisfying the above-mentionedcondition (2) to be used in the first lens unit L₁ of the objective lenssystem according to the present invention is expressed by the formulagiven below, it is desirable to satisfy at least either one of theconditions that at least one of the aspherical surface coefficients ofthe fourth and higher orders E, F, G, H, . . . is positive when saidaspherical surface is located on the object side and that at least oneof the aspherical surface coefficients is negative when said asphericalsurface is located on the image side: ##EQU7## the reference symbols xand y represent values of coordinates on which the direction along theoptical axis is regarded as the x axis taKing the direction toward animage as positive, intersection between the aspherical surface and theoptical axis is considered as the origin, and the directionperpendicular to the axis is considered as y axis, and the referencesymbol C designates an inverse number of radius of curvature of a circlein contact with the aspherical surface in the vicinity of the opticalaxis.

The aspherical surface to be used in the objective lens system forendoscopes according to the present invention is sufficient so far as itsatisfies the condition (2) and at least one of the aspherical surfacecoefficients E, F, G, . . . , which may have various values, must have apositive value.

When a prism or mirror for changing field direction by bending theoptical axis for side viewing is to be arranged between the first lensunit and the second lens unit in the objective lens system forendoscopes according to the present invention, it is desirable to designthe lens system so as to satisfy the following condition (10): ##EQU8##wherein the reference symbol d represents distance as measured from thesurface located on the extremely image side out of the surfaces havingrefractive powers in the first lens unit to the surface located on theextremely object side out of the surfaces having refractive powers inthe second lens unit.

If d has a value smaller than the lower limit of the condition (10), theobjective lens system will not permit reserving the airspace forarranging said prism or mirror. If d has a value larger than the upperlimit of the condition (10), in contrast, the airspace reserved betweenthe first lens unit and the second lens unit will be wide, therebymaKing it difficult to correct aberrations favorably.

It is possible by changing shape of said prism to compose objective lenssystems having various field directions. Examples of said prism areshown in FIG. 3 (A), FIG. 3 B and FIG. 3 C wherein the reflectingsurfaces are designed as totally reflecting surfaces or surfaces coatedwith metallic films for reflecting the effective rays. In FIG. 3 C , thereference symbol S represents a stop fixed to a prism.

Further, it is difficult to shape, by grinding, the lens element havingthe aspherical surface on the object side and to be arranged in thefirst lens unit. Accordingly, the aspherical lens element is to beshaped by molding or cutting. It is therefore desirable to design theaspherical lens element so as to have a shape manufacturable relativelyeasily. Hence, the aspherical lens element should desirably have animage side surface which is plane or has a relatively large radius ofcurvature as shown in FIG. 19. And, it is also desirable to design thefirst lens unit so as to have such a composition wherein a lens elementhaving negative refractive power is located in the vicinity of the imageside surface or cemented thereto.

By selecting adequate refractive indices and dispersing powers for theplural number of lens elements arranged in the vicinity of each other orcemented to each other as described above in the first lens unit, it ispossible to correct chromatic aberration and other aberrationsfavorably.

Furthermore, though glass, plastics and optical crystals such assapphire may be considered as materials for the aspherical lens element,it is desirable to select glass from the viewpoints of manufacturingcost and resistance to temperature, humidity, chemicals, etc., and shapethe aspherical lens component by molding glass.

Moreover, the objective lens system for endoscopes according to thepresent invention is designed in such a manner that optical path lengthz: between the surface located on the extremely image side out of thesurfaces having negative refractive powers in the first lens unit L: andthe surface located on the extremely object side out of the surfaceshaving positive refractive powers in the second lens unit L₂ satisfiesthe following condition (7):

    z.sub.1 /f≧1                                        (7)

In the objective lens system for endoscopes according to the presentinvention, the first lens unit L₁ comprises at least one asphericalsurface for correcting distortion sufficiently. The surface concave onthe object side and Kept in contact with air in the second lens unit L₂has a function to produce positive curvature of field in the objectivelens system and is capable of correcting sufficiently favorably thecurvature of field to be produced by the relay lens system.

Further, the condition (7) is required to reserve a space allowing toarrange a field direction changing system between the first lens unit L₁and the second lens unit L₂. If the condition (7) is not satisfied, itwill be impossible to arrange a field direction changing system in theobjective lens system for endoscopes according to the present invention,thereby disabling to accomplish one of the objects of the presentinvention. It is desirable for composing the field direction changingsystem to use a glass material having relatively high refractive indexso as to provide a long optical path length.

Furthermore, in order to shorten outside diameter of the objective lenssystem by lowering height of the principal ray, it is desirable todesign the objective lens system so as to satisfy the followingcondition (8):

    z.sub.2 /z.sub.1 ≦0.8                               (8)

wherein the reference symbol z₂ represents optical path length asmeasured from the surface arranged on the extremely image side out ofthe surfaces having negative refractive powers in the first lens unit L₁to the front focal point of the second lens unit L₂.

Since a non-flexible endoscope has the shape of a long bar, outsidediameters must be nearly the same between the objective lens system andthe relay lens systems to be used in the non-flexible endoscope.

It is necessary also for the objective lens system for endoscopesaccording to the present invention to prevent heights of rays from beingtoo high on the respective lens elements.

In order to minimize loss of light quantity at the stage of incidence onthe relay lens systems, the objective lens system for endoscopes isdesigned in such a manner that the principal ray is perpendicular to theimage surface as described above. For this purpose, the objective lenssystem for endoscopes according to the present invention is so composedas to allow the principal ray to intersect with the optical axis in thevicinity of the front focal point of the second lens unit L₂.Accordingly, it is possible to lower height of the principal ray on thefirst lens unit L₁ by shortening the optical path length as measuredfrom the surface arranged on the extremely image side out of thesurfaces having negative refractive powers in the first lens unit L₁ tothe front focal point of the second lens unit L₂.

If the condition (8) is not satisfied, height of the principal ray willbe increased on the first lens unit L₁, thereby enlarging outsidediameter of the first lens unit L₁ and maKing the objective lensunsuited for use with endoscopes.

In order to reduce distortion at a wide field angle, it is desirable todesign the objective lens system for endoscopes according to the presentinvention so as to satisfy the following condition (9):

    |f.sub.2 /f.sub.1 |≦8             (9)

wherein the reference symbols f₁ and f₂ represent focal lengths of thefirst lens unit L₁ and the second lens unit L₂ respectively.

Distortion is produced due to the fact that the principal ray isrefracted in the direction to widen the field angle by the negativestrong refractive power of the first lens unit L₁. In order to minimizedistortion at a wide field angle, it is therefore desirable torelatively weaKen the negative strong refractive power of the first lensunit L₁ and relatively strengthen the positive refractive power of thesecond lens unit L₂. This means relatively increases the inclination,with regard to the optical axis, of the principal ray between the firstlens unit L₁ and the second lens unit L₂.

If f₂ is too long to satisfy the condition (9), the objective lenssystem as a whole will have too weaK refractive power and cannot have awide field angle, or if f₁ is too short to satisfy the condition (9),the first lens unit L₁ will have too strong negative refractive power,thereby maKing it difficult to correct distortion.

The objective lens system for endoscopes according to the presentinvention comprises, on the extremely object side in the second lensunit L₂, a bar-shaped lens component which is longer in the directionalong the optical axis than in the diametrical direction. It is possibleto arrange the field direction changing optical system by utilizing aportion of the bar-shaped lens component. The objective lens system forendoscopes according to the present invention has such a composition asto accurately locate the field direction changing optical system. Thefield direction changing optical system to be used in the objective lenssystem for endoscopes according to the present invention consists, forexample, of a field direction changing prism having a refracting surfaceand a reflecting surface, and a stabilizing optical element capable ofarranging said prism at an accurately positioned state. The fielddirection changing prism refracts the rays incident thereon by therefracting surface thereof, reflects the rays by the reflecting surfacethereof, reflects the rays by said refracting surface and then allowsthe rays to emerge from the emerging surface thereof. The prism changesthe field direction by differenciating the direction of the incidentrays from that of the emerging rays. Further, the rays emerging from thefield direction changing prism fall on the stabilizing optical element.In the field direction changing optical system, the field directionchanging prism and the stabilizing optical element are arranged in sucha manner that the shapes and sizes of a sectional surfaces perpendicularto the optical axis are the same between the field direction changingprism and the stabilizing optical element, that the surface of emergenceof the field direction changing prism is parallel to the surface ofincidence of the stabilizing optical element, and that both the surfacesare Kept in contact with each other or located in the vicinity of eachother.

FIG. 20 illustrates a fundamental composition of the field directionchanging optical system to be used in the objective lens system forendoscopes according to the present invention. The field directionchanging optical system consists of a field direction changing prism 1and a stabilizing optical element 3 and is adapted in such a manner thatan oblique ray l is refracted by a refracting surface 1_(b), reflectedby a reflecting surface 1_(a), reflected by the refractive surface1_(b), emerges from the emerging surface (reflecting surface 1_(a)) andthen falls on the stabilizing optical element 3.

The sectional shape and size of the field direction changing prism 1 arethe same as those of the stabilizing optical system so that the outercircumferential surfaces of these member form a continuous surface asshown in FIG. 20. That is to say, it is possible to form the fielddirection changing prism and the stabilizing optical element by cutting,along a surface inclined with regard to the optical axis, the bar-shapedlens component to be used in the objective lens system for endoscopesaccording to the present invention. Accordingly, it is possible, whenthe outer circumferential surfaces of the field direction changing prism1 and the stabilizing optical element 3 (i.e., the bar-shaped lenscomponent) is preliminarily matched accurately with the inner surface ofa distal end frame of an endoscope, to correctly position these memberssimply by sequentially setting these members into the distal end frameof the endoscope with no misalignment between the central axes thereofnor inclination of the cemented surfaces thereof.

FIG. 21 exemplifies a case where a correcting prism 2 is arranged inaddition to the field direction changing prism 1. Also in this case, thecomponent members of the field direction optical system can be arrangedcorrectly in the procedures similar to those described with reference toFIG. 20.

When diameter of the sectional surface perpendicular to the longitudinalaxis of the endoscope is represented by D and length of the longitudinalcenter axis is designated by T, it is desirable for the field directionchanging optical systems shown in FIG. 20 and FIG. 21 to satisfy thefollowing condition:

    1.2<T/D<4

If T/D is smaller than 1.2, the field direction changing prism allowsremarKable positional deviation, thereby undesirably deviating the fielddirection and producing astigmatism. If T/D is larger than 4, theoptical path length will be prolonged in the prism and rays will bediverged to enhance height of rays on the surface of emergency of thestabilizing optical element, thereby allowing the rays to be eclipsedand images to be darKened in the endoscope which cannot have a largeoutside diameter.

In addition, the field direction changing optical systems shown in FIG.20 and FIG. 21 can be prepared, for example, by modifying the secondlens unit L₂ shown in FIG. 13. SpeaKing concretely, the positive lenscomponent arranged on the extremely object side in the second lens unitL₂ can be composed of three blocKs of the correcting prism 2, the fielddirection changing prism 1 and the stabilizing optical element 3.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 and FIG. 2 show sectional views illustrating the conventionalobjective lens systems for endoscopes;

FIG. 3A, FIG. 3B and FIG. 3C show sectional views of the conventionalobjective lens systems for endoscopes comprising field directionchanging prisms;

FIG. 4 shows a sectional view illustrating the conventional opticalsystem for non-flexible endoscopes;

FIG. 5 shows graphs illustrating aberration characteristics of theoptical system shown in FIG. 4;

FIG. 6 shows graphs illustrating relationship between inclination angleof the principal ray and aberrations in the conventional objective lenssystems for endoscopes;

FIG. 7 shows a sectional view illustrating travelling course of theprincipal ray in the conventional objective lens systems for endoscopes;

FIG. 8 and FIG. 9 show images of lattice patterns formed by opticalsystems having 0% and 30% of distortion respectively;

FIG. 10 shows a sectional view illustrating a photographic lens systemhaving little distortion;

FIG. 11 and FIG. 12 show sectional views illustrating the conventionalfield direction changing optical systems for oblique viewing;

FIG. 13 shows a sectional view illustrating the fundamental compositionof the objective lens system for endoscopes according to the presentinvention;

FIG. 14A and FIG. 14B show diagrams illustrating conditions of theprincipal ray refracted by aspherical surfaces;

FIG. 15A, FIG. 15B, FIG. 15C and FIG. 15D show distortions correspondingrespectively to the conditions of the principal ray refracted by theaspherical surfaces;

FIG. 16 shows a sectional view illustrating of a distal end of anon-flexible endoscope comprising the objective lens system according tothe present invention;

FIG. 17 shows a diagram illustrating relationship between an asphericalsurface and travelling course of the principal ray in the objective lenssystem for endoscopes according to the present invention;

FIG. 18A and FIG. 18B show diagrams illustrating condition of theprincipal ray refracted by the aspherical surface used in the objectivelens system according to the present invention;

FIG. 19 show a diagram exemplifying shape of the aspherical surface;

FIG. 20 and FIG. 21 show sectional views illustrating field directionchanging optical systems to be arranged in the objective lens systemaccording to the present invention;

FIG. 22 through FIG. 53 show sectional views illustrating Embodiments 1through 32 of the objective lens system for endoscopes according to thepresent invention; and

FIG. 54 through FIG. 85 show graphs illustrating aberrationcharacteristics of the Embodiments 1 through 32.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the present invention will be described more detailedly below withreference to the accompanying drawings and the numerical data shownbelow in the form of numerical data:

    ______________________________________                                        Embodiment 1                                                                  f = 1.000, F/5.163, 2ω = 67.31°                                  IH = 0.68, object distance = -8.8496                                          ______________________________________                                        r.sub.1  = ∞                                                                        d.sub.1 = 0.0885                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.0590                                                  r.sub.3 = 4.8865                                                              (aspherical surface)                                                                      d.sub.3 = 0.3835                                                                         n.sub.2 = 1.78472                                                                         ν.sub.2 = 25.71                         r.sub.4 = ∞                                                                         d.sub.4 = 0.1180                                                                         n.sub.3 = 1.58144                                                                         ν.sub.3 = 40.75                         r.sub.5 = 0.3540                                                                          d.sub.5 = 0.2360                                                  r.sub.6 = ∞                                                                         d.sub.6 = 0.7563                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = ∞ (stop)                                                                  d.sub.7 = 2.0048                                                                         n.sub.5 = 1.80610                                                                         ν.sub.5 = 40.95                         r.sub.8 = -1.2746                                                                         d.sub.8 = 0.0885                                                  r.sub.9 = 2.4460                                                                          d.sub.9 = 0.8850                                                                         n.sub.6 = 1.60311                                                                         ν.sub.6 = 60.70                         r.sub.10 = -0.9310                                                                        d.sub.10 = 0.2950                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.88                         r.sub.11 = -4.0838                                                                        d.sub.11 = 0.8348                                                 r.sub.12 = -0.8024                                                                        d.sub.12 = 0.2950                                                                        n.sub.8 = 1.58144                                                                         ν.sub.8 = 40.75                         r.sub.13 = ∞                                                                        d.sub.13 = 0.6785                                                                        n.sub.9 = 1.60311                                                                         ν.sub.9 = 60.70                         r.sub.14 = -1.1749                                                            aspherical coefficient                                                        E = 0.22613, F = -0.16693 p = 1                                               |R.sub.1 | = 0.354, ΔK = 0.037                         ##STR1##                                                                     h.sub.1 /I.sub.max = 0.677, |R.sub.min | = 0.354,           f.sub.2 = 1.802                                                               tan α = 0.1485, tan ω.sub.1 = 0.666                               ______________________________________                                        Embodiment 2                                                                  f = 1.000, F/6.081, 2ω = 69.97°                                  IH = 0.6686, object distance = -17.2911                                       ______________________________________                                        r.sub.1  = ∞                                                                        d.sub.1 = 0.2305                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.1153                                                  r.sub.3 = 2.1028                                                              (aspherical surface)                                                                      d.sub.3 = 0.2882                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = 0.4496                                                                          d.sub.4 = 0.2305                                                  r.sub.5 = ∞                                                                         d.sub.5 = 0.7927                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 =  40.95                        r.sub.6 = ∞ (stop)                                                                  d.sub.6 = 2.2044                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = -1.2922                                                                         d.sub.7 = 0.1729                                                  r.sub.8 = 2.8519                                                                          d.sub.8 = 1.0663                                                                         n.sub.5 = 1.60311                                                                         ν.sub.5 = 60.70                         r.sub.9 = -1.0767                                                                         d.sub.9 = 0.2305                                                                         n.sub.6 = 1.84666                                                                         ν.sub.6 = 23.78                         r.sub.10 = -3.0726                                                                        d.sub.10 = 0.2882                                                 r.sub.11 = -0.9798                                                                        d.sub.11 = 0.3458                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.78                         r.sub.12 = -9.2888                                                                        d.sub.12 = 0.1556                                                 r.sub.13 = 2.6974                                                                         d.sub.13 = 0.6282                                                                        n.sub.8 = 1.65160                                                                         ν.sub.8 = 58.52                         r.sub.14 = -2.6974                                                            aspherical coefficient                                                        E = 0.20175, F = -0.65172 × 10.sup.- 2, p = 1                           |R.sub.1 | = 0.4496, ΔK = 0.058                        ##STR2##                                                                     h.sub.1 /I.sub.max = 0.542, |R.sub.min | = 0.4496,          f.sub.2 = 1.697                                                               tan α = 0.2137, tan ω.sub.1 = 0.700                               ______________________________________                                        Embodiment 3                                                                  f = 1.000, F/6.109, 2ω = 70.14°                                  IH = 0.67, object distance = -17.3110                                         ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.2308                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.1154                                                  r.sub.3 = 2.1052                                                              (aspherical surface)                                                                      d.sub.3 = 0.2885                                                                         n.sub.2 =  1.78472                                                                        ν.sub.2 = 25.71                         r.sub.4 = 0.4385                                                                          d.sub.4 = 0.2308                                                  r.sub.5 = ∞                                                                         d.sub.5 = 0.7933                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.6 = ∞ (stop)                                                                  d.sub.6 = 2.2073                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = -1.2937                                                                         d.sub.7 = 0.1731                                                  r.sub.8 = 2.8552                                                                          d.sub.8 = 1.0675                                                                         n.sub.5 = 1.60311                                                                         ν.sub.5 = 60.70                         r.sub.9 = -1.0779                                                                         d.sub.9 = 0.2308                                                                         n.sub.6 = 1.84666                                                                         ν.sub.6 = 23.78                         r.sub.10 = -3.0744                                                                        d.sub.10 = 0.2885                                                 r.sub.11 = -0.9781                                                                        d.sub.11 = 0.3462                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.78                         r.sub.12 = -9.2995                                                                        d.sub.12 = 0.1558                                                 r.sub.13 = 2.7005                                                                         d.sub.13 = 0.6290                                                                        n.sub.8 = 1.65160                                                                         ν.sub.8 = 58.67                         r.sub.14 = -2.7005                                                            aspherical coefficient                                                        E = 0.20105, F = -0.64797 × 10.sup.-2, p = 1                            |R.sub.1 | = 0.4385, ΔK = 0.059                        ##STR3##                                                                     h.sub.1 /I.sub.max = 0.544, |R.sub.min | = 0.4385,          f.sub.2 = 1.699                                                               tan α = 0.2143, tan ω.sub.1 = 0.702                               ______________________________________                                        Embodiment 4                                                                  f = 1.000, F/7.153, 2ω = 70.14°                                  IH = 0.67, object distance = -17.4331                                         ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.2324                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.1162                                                  r.sub.3 = 2.7796                                                              (aspherical surface)                                                                      d.sub.3 = 0.5035                                                                         n.sub.2 = 1.78472                                                                         ν.sub.2 = 25.71                         r.sub.4 = 0.4416                                                                          d.sub.4 = 0.2324                                                  r.sub.5 = ∞                                                                         d.sub.5 = 1.2018                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.6 = ∞ (stop)                                                                  d.sub.6 = 1.8199                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = -1.3028                                                                         d.sub.7 = 0.1743                                                  r.sub.8 = 2.8753                                                                          d.sub.8 = 1.0750                                                                         n.sub.5 = 1.60311                                                                         ν.sub.5 = 60.70                         r.sub.9 = -1.0855                                                                         d.sub.9 = 0.2324                                                                         n.sub.6 = 1.84666                                                                         ν.sub.6 = 23.78                         r.sub.10 = -3.0961                                                                        d.sub.10 = 0.2906                                                 r.sub.11 = -0.9850                                                                        d.sub.11 = 0.3487                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.78                         r.sub.12 = -9.3650                                                                        d.sub.12 = 0.1569                                                 r.sub.13 = 2.7196                                                                         d.sub.13 = 0.6334                                                                        n.sub.8 = 1.65160                                                                         ν.sub.8 = 58.67                         r.sub.14 = -2.7196                                                            aspherical coefficient                                                        E = 0.14395, F = -0.62561 × 10.sup.-2, p = 1                            |R.sub.1 | = 0.4416, ΔK = 0.037                        ##STR4##                                                                     h.sub.1 /I.sub.max = 0.769, |R.sub.min | = 0.4416,          f.sub.2 = 1.711                                                               tan α = 0.2686, tan ω.sub.1 = 0.702                               ______________________________________                                        Embodiment 5                                                                  f = 1.000, F/8.155, 2ω = 70.14°                                  IH = 0.68, object distance = -17.5213                                         ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.2336                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.1168                                                  r.sub.3 = 4.2913                                                              (aspherical surface)                                                                      d.sub.3 = 1.0121                                                                         n.sub.2 = 1.78472                                                                         ν.sub.2 = 25.71                         r.sub.4 = 0.4439                                                                          d.sub.4 = 0.2336                                                  r.sub.5 = ∞                                                                         d.sub.5 = 1.5341                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.6 = ∞ (stop)                                                                  d.sub.6 = 1.5029                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = -1.3094                                                                         d.sub.7 = 0.1752                                                  r.sub.8 = 2.8898                                                                          d.sub.8 = 1.0805                                                                         n.sub.5  = 1.60311                                                                        ν.sub.5 = 60.70                         r.sub.9 = -1.0910                                                                         d.sub.9 = 0.2336                                                                         n.sub.6 = 1.84666                                                                         ν.sub.6 = 23.78                         r.sub.10 = -3.1118                                                                        d.sub.10 = 0.2920                                                 r.sub.11 = -0.9900                                                                        d.sub.11 = 0.3504                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.78                         r.sub.12 = -9.4124                                                                        d.sub.12 = 0.1577                                                 r.sub.13 = 2.7333                                                                         d.sub.13 = 0.6366                                                                        n.sub.8 = 1.65160                                                                         ν.sub.8 = 58.67                         r.sub.14 = -2.7333                                                            aspherical coefficient                                                        E = 0.59647 × 10.sup.-1, F = -0.61002 × 10.sup.-2, p = 1          |R.sub.1 | = 0.4439, ΔK = 0.023                        ##STR5##                                                                     h.sub.1 /I.sub.max = 1.176, |R.sub.min | = 0.4439,          f.sub.2 = 1.720                                                               tan α = 0.2973, tan ω.sub.1 = 0.702                               ______________________________________                                        Embodiment 6                                                                  f = 1.000, F/5.200, 2ω = 66.99°                                  IH = 0.6062, object distance = -8.3426                                        ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.0834                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.0556                                                  r.sub.3 = 4.6851                                                              (aspherical surface)                                                                      d.sub.3 = 0.3615                                                                         n.sub.2 = 1.78472                                                                         ν.sub.2 = 25.71                         r.sub.4 = ∞                                                                         d.sub.4 = 0.1112                                                                         n.sub.3 = 1.58144                                                                         ν.sub.3 = 40.75                         r.sub.5 = 0.3337                                                                          d.sub.5 = 0.2225                                                  r.sub.6 =  ∞                                                                        d.sub.6 = 0.7131                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = ∞ (stop)                                                                  d.sub.7 = 1.8898                                                                         n.sub.5 = 1.80610                                                                         ν.sub.5 = 40.95                         r.sub.8 = -1.2954                                                                         d.sub.8 = 0.0834                                                  r.sub.9 = 1.7066                                                                          d.sub.9 = 0.8343                                                                         n.sub.6 = 1.60311                                                                         ν.sub.6 = 60.70                         r.sub.10 = -0.9557                                                                        d.sub.10 = 0.2781                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.88                         r.sub.11 = -7.5841                                                                        d.sub.11 = 0.8089                                                 r.sub.12 = -0.6839                                                                        d.sub.12 = 0.2781                                                                        n.sub.8 = 1.58144                                                                         ν.sub.8 = 40.75                         r.sub.13 = ∞                                                                        d.sub.13 = 0.6396                                                                        n.sub.9 = 1.60311                                                                         ν.sub.9 = 60.70                         r.sub.14 = -1.0340                                                            aspherical coefficient                                                        E = 0.20085, F =  -0.22420, p = 1                                             |R.sub.1 | = 0.3337, ΔK = 0.051                        ##STR6##                                                                     h.sub.1 /I.sub.max = 0.652, |R.sub.min | = 0.3337,          f.sub.2 = 1.733                                                               tan α = 0.1213, tan ω.sub.1 = 0.661                               ______________________________________                                        Embodiment 7                                                                  f = 1.000, F/5.210, 2ω = 67.67°                                  IH = 0.6714, object distance = -9.2393                                        ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.0924                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.0616                                                  r.sub.3 = 6.0741                                                              (aspherical surface)                                                                      d.sub.3 = 0.4004                                                                         n.sub.2 =  1.78472                                                                        ν.sub.2 = 25.71                         r.sub.4 = ∞                                                                         d.sub.4 = 0.1232                                                                         n.sub.3 = 1.58144                                                                         ν.sub.3 = 40.75                         r.sub.5 = 0.3696                                                                          d.sub.5 = 0.2464                                                  r.sub.6 = ∞                                                                         d.sub.6 = 0.7894                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = ∞ (stop)                                                                  d.sub.7 = 2.0932                                                                         n.sub.5 = 1.80610                                                                         ν.sub.5 = 40.95                         r.sub.8 = -1.2770                                                                         d.sub.8 = 0.0924                                                  r.sub.9 = 3.0909                                                                          d.sub.9 = 0.9239                                                                         n.sub.6 = 1.60311                                                                         ν.sub.6 = 60.70                         r.sub.10 = -0.9192                                                                        d.sub.10 = 0.3080                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.88                         r.sub.11 = -3.2067                                                                        d.sub.11 = 0.8442                                                 r.sub.12 = -0.7998                                                                        d.sub.12 = 0.3080                                                                        n.sub.8 =  1.58144                                                                        ν.sub.8 = 40.75                         r.sub.13 = ∞                                                                        d.sub.13 = 0.7083                                                                        n.sub.9 = 1.60311                                                                         ν.sub.9 = 60.70                         r.sub.14 = -1.2141                                                            aspherical coefficient                                                        E = 0.23807, F = -0.13456, p = 1                                              |R.sub.1 | = 0.3696, ΔK = 0.027                        ##STR7##                                                                     h.sub.1 /I.sub.max = 0.684, |R.sub.min | = 0.3696,          f.sub.2 = 1.865                                                               tan α = 0.1514, tan ω.sub.1 = 0.670                               ______________________________________                                        Embodiment 8                                                                  f = 1.000, F/5.240, 2ω = 87.49°                                  IH = 0.9152, object distance = -12.5945                                       ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.1259                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.0840                                                  r.sub.3 = -647.3792                                                           (aspherical surface)                                                                      d.sub.3 = 0.5458                                                                         n.sub.2 = 1.78472                                                                         ν.sub.2 = 25.71                         r.sub.4 = ∞                                                                         d.sub.4 = 0.1679                                                                         n.sub.3 = 1.58144                                                                         ν.sub.3 = 40.75                         r.sub.5 = 0.5038                                                                          d.sub.5 = 0.3359                                                  r.sub.6 = ∞                                                                         d.sub.6 = 1.0759                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = ∞ (stop)                                                                  d.sub.7 = 2.8535                                                                         n.sub.5 = 1.80610                                                                         ν.sub.5 = 40.95                         r.sub.8 = -1.7455                                                                         d.sub.8 = 0.1259                                                  r.sub.9 = 4.0568                                                                          d.sub.9 = 1.2594                                                                         n.sub.6 = 1.60300                                                                         ν.sub.6 = 65.48                         r.sub.10 =  -1.2564                                                                       d.sub.10 = 0.4198                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.88                         r.sub.11 = -3.0412                                                                        d.sub.11 = 0.6504                                                 r.sub.12 = -1.4735                                                                        d.sub.12 = 0.4198                                                                        n.sub.8 = 1.59270                                                                         ν.sub.8 = 35.29                         r.sub.13 = ∞                                                                        d.sub.13 = 0.9656                                                                        n.sub.9 = 1.51728                                                                         ν.sub.9 = 69.56                         r.sub.14 = -1.9745                                                            aspherical coefficient                                                        E = 0.10039, F = -0.28591 × 10.sup.-1, p = 1                            |R.sub.1 | = 0.5038, ΔK = 0.052                        ##STR8##                                                                     h.sub.1 /I.sub.max = 0.858, |R.sub.min | = 0.5038,          f.sub.2  = 2.139                                                              tan α = 0.1443, tan ω.sub.1 = 0.957                               ______________________________________                                        Embodiment 9                                                                  f = 1.000, F/5.062, 2ω = 87.10°                                  IH = 0.8613, object distance = -11.8530                                       ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.1185                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.0790                                                  r.sub.3 = -56.3732                                                            (aspherical surface)                                                                      d.sub.3 = 0.5136                                                                         n.sub.2 = 1.78472                                                                         ν.sub.2 = 25.71                         r.sub.4 = ∞                                                                         d.sub.4 = 0.1580                                                                         n.sub.3 = 1.58144                                                                         ν.sub.3 = 40.75                         r.sub.5 = 0.4741                                                                          d.sub.5 = 0.3161                                                  r.sub.6 = ∞                                                                         d.sub.6 = 1.0124                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = ∞ (stop)                                                                  d.sub.7 =  2.6857                                                                        n.sub.5 = 1.80610                                                                         ν.sub.5 = 40.95                         r.sub.8 = -1.7177                                                                         d.sub.8 = 0.1185                                                  r.sub.9 = 2.9925                                                                          d.sub.9 = 1.1853                                                                         n.sub.6 = 1.60300                                                                         ν.sub.6 = 65.48                         r.sub.10 = -1.3612                                                                        d.sub.10 = 0.3951                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.88                         r.sub.11 = -3.8561                                                                        d.sub.11 = 0.6970                                                 r.sub.12 = -1.1928                                                                        d.sub.12 = 0.3951                                                                        n.sub.8 = 1.59270                                                                         ν.sub.8 = 35.29                         r.sub.13 = ∞                                                                        d.sub.13 = 0.9087                                                                        n.sub.9 = 1.51728                                                                         ν.sub.9 = 69.56                         r.sub.14 = -1.6083                                                            aspherical coefficient                                                        E = 0.11335, F = -0.38725 × 10.sup.-1, p = 1                            |R.sub.1 | = 0.4741, ΔK = 0.063                        ##STR9##                                                                     h.sub.1 /I.sub.max = 0.821, |R.sub.min | = 0.4741,          f.sub.2 = 2.090                                                               tan α = 0.1316, tan ω.sub.1 = 0.951                               ______________________________________                                        Embodiment 10                                                                 f = 1.000, F/5.259, 2ω = 87.99°                                  IH = 0.9629, object distance = -13.2509                                       ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.1325                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.0883                                                  r.sub.3 = -12.8271                                                            (aspherical surface)                                                                      d.sub.3 = 0.5742                                                                         n.sub.2 = 1.78472                                                                         ν.sub.2 = 25.71                         r.sub.4 = ∞                                                                         d.sub.4 = 0.1767                                                                         n.sub.3 =  1.58144                                                                        ν.sub.3 = 40.75                         r.sub.5 = 0.5300                                                                          d.sub.5 = 0.3534                                                  r.sub.6 = ∞                                                                         d.sub.6 = 1.1318                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = ∞ (stop)                                                                  d.sub.7 = 3.0025                                                                         n.sub.5 = 1.80610                                                                         ν.sub.5 = 40.95                         r.sub.8 = -1.6269                                                                         d.sub.8 = 0.1325                                                  r.sub.9 = 5.9867                                                                          d.sub.9 = 1.3251                                                                         n.sub.6 = 1.60300                                                                         ν.sub.6 = 65.48                         r.sub.10 = -1.0538                                                                        d.sub.10 = 0.4417                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.88                         r.sub.11 = -2.8854                                                                        d.sub.11 = 0.6843                                                 r.sub.12 = -1.4437                                                                        d.sub.12 = 0.4417                                                                        n.sub.8 = 1.59270                                                                         ν.sub.8 = 35.29                         r.sub.13 = ∞                                                                        d.sub.13 = 1.0159                                                                        n.sub.9 = 1.51728                                                                         ν.sub.9 = 69.56                         r.sub.14 = -1.8947                                                            aspherical coefficient                                                        E = 0.10389, F = -0.22176 × 10.sup.-1, p = 1                            |R.sub.1 | = 0.5300, ΔK = 0.039                        ##STR10##                                                                    h.sub.1 /I.sub.max = 0.836, |R.sub.min | = 0.5300,          f.sub.2 = 2.301                                                               tan α = 0.2344, tan ω.sub.1 = 0.966                               ______________________________________                                        Embodiment 11                                                                 f = 1.000, F/6.051, 2ω = 69.86°                                  IH = 0.6674, object distance = -17.2612                                       ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.1726                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub. 2 = ∞                                                                        d.sub.2 = 0.1151                                                  r.sub.3 = 2.4550                                                              (aspherical surface)                                                                      d.sub.3 = 0.2877                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = 0.4488                                                                          d.sub.4 = 0.2301                                                  r.sub.5 = ∞                                                                         d.sub.5 = 0.9394                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.6 = ∞ (stop)                                                                  d.sub.6 = 2.0525                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = -1.2900                                                                         d.sub.7 = 0.1726                                                  r.sub.8 = 3.7635                                                                          d.sub.8 = 1.1507                                                                         n.sub.5 = 1.60311                                                                         ν.sub.5 = 60.70                         r.sub.9 = -1.0598                                                                         d.sub.9 = 0.2301                                                                         n.sub.6 = 1.84666                                                                         ν.sub.6 = 23.78                         r.sub.10 = -1.9350                                                                        d.sub.10 = 0.4603                                                 r.sub.11 = -0.6904                                                                        d.sub.11 = n.sub.7 = 1.78472                                                                         ν.sub.7 = 25.71                         r.sub.12 = ∞                                                                        d.sub.12 = 0.7250                                                                        n.sub.8 = 1.69680                                                                         ν.sub.8 = 55.52                         r.sub.13 = -1.1438                                                            aspherical coefficient                                                        E = 0.19848, F = 0.39318 × 10.sup.-5, p = 1                             |R.sub.1 | = 0.4488, ΔK = 0.055                        ##STR11##                                                                    H.sub.1 /I.sub.max = 0.550, |R.sub.min | = 0.4488,          f.sub.2 = 1.964                                                               tan α = 0.1902, tan ω.sub.1 = 0.698                               ______________________________________                                        Embodiment 12                                                                 f = 1.000, F/6.080, 2ω = 70.02°                                  IH = 0.6686, object distance = -28.8184                                       ______________________________________                                        r.sub.1  = ∞                                                                        d.sub.1 = 0.1729                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.1153                                                  r.sub.3 = 3.0173                                                              (aspherical surface)                                                                      d.sub.3 = 0.2882                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = 0.4233                                                                          d.sub.4 = 0.2882                                                  r.sub.5 = ∞                                                                         d.sub.5 = 1.7036                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.6 = ∞ (stop)                                                                  d.sub.6 = 2.1786                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = -1.9237                                                                         d.sub.7 = 0.2882                                                  r.sub.8 = 23.0048                                                                         d.sub.8 = 1.0029                                                                         n.sub.5 = 1.64000                                                                         ν.sub.5 = 60.09                         r.sub.9 = -1.0650                                                                         d.sub.9 = 0.2478                                                                         n.sub.6 = 1.84666                                                                         ν.sub.6 = 23.88                         r.sub.10 = -2.1708                                                                        d.sub.10 = 2.0402                                                 r.sub.11 = -0.9691                                                                        d.sub.11 = 0.5764                                                                        n.sub.7 = 1.64769                                                                         ν.sub.7 = 33.80                         r.sub.12 = ∞                                                                        d.sub.12 = 0.5648                                                                        n.sub.8 = 1.78800                                                                         ν.sub.8 = 47.38                         r.sub.13 = -1.6391                                                            aspherical coefficient                                                        E = 0.27896, F = 0.17497 × 10.sup.-5, p = 1                             |R.sub.1 | = 0.4233, ΔK = 0.029                        ##STR12##                                                                    h.sub.1 /I.sub.max = 0.629, |R.sub.min | = 0.4233,          f.sub.2 = 2.805                                                               tan α = 0.2272, tan ω.sub.1 = 0.701                               ______________________________________                                        Embodiment 13                                                                 f = 1.000, F/5.965, 2ω = 73.60°                                  IH = 0.7432, object distance = -18.1269                                       ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.2417                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.1208                                                  r.sub.3 = 1.7634                                                              (aspherical surface)                                                                      d.sub.3 = 0.3021                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = 0.4713                                                                          d.sub.4 = 0.2417                                                  r.sub.5 = ∞                                                                         d.sub.5 = 0.8472                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.6 = ∞ (stop)                                                                  d.sub.6 = 2.2948                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = -1.5109                                                                         d.sub.7 = 0.1813                                                  r.sub.8 = 4.3329                                                                          d.sub.8 = 1.1178                                                                         n.sub.5 = 1.60311                                                                         ν.sub.5 = 60.70                         r.sub.9 = -1.2674                                                                         d.sub.9 = 0.2417                                                                         n.sub.6 = 1.84666                                                                         ν.sub.6 = 23.78                         r.sub.10 = -1.8784                                                                        d.sub.10 = 0.3021                                                 r.sub.11 = -1.2270                                                                        d.sub.11 = 0.3625                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.78                         r.sub.12 = -5.7567                                                                        d.sub.12 = 0.1631                                                 r.sub.13 = 6.2536                                                                         d.sub.13 = 0.6586                                                                        n.sub.8 = 1.65160                                                                         ν.sub.8 = 58.52                         r.sub.14 = -3.4067                                                            aspherical coefficient                                                        E = 0.17732, F = -0.51470 × 10.sup.-2, p = 1                            |R.sub.1 | = 0.4713, ΔK = 0.060                        ##STR13##                                                                    h.sub.1 /I.sub.max = 0.579, |R.sub. min | = 0.4713,         f.sub.2 = 1.757                                                               tan α = 0.3070, tan ω.sub.1 = 0.748                               ______________________________________                                        Embodiment 14                                                                 f = 1.000, F/6.564, 2ω = 74.77°                                  IH = 0.6718, object distance = -16.3845                                       ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.1638                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.1092                                                  r.sub.3 = 3.8668                                                              (aspherical surface)                                                                      d.sub.3 = 0.2731                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = 0.4260                                                                          d.sub.4 = 0.2185                                                  r.sub.5 = ∞                                                                         d.sub.5 = 0.8806                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.6 = ∞ (stop)                                                                  d.sub.6 = 1.9593                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 =  -1.7675                                                                        d.sub.7 = 0.1638                                                  r.sub.8 = 2.7768                                                                          d.sub.8 = 1.0923                                                                         n.sub.5 = 1.60311                                                                         ν.sub.5 = 60.70                         r.sub.9 = -0.9650                                                                         d.sub.9 = 0.2185                                                                         n.sub.6 = 1.84666                                                                         ν.sub.6 = 23.78                         r.sub.10 = -1.5214                                                                        d.sub.10 = 0.9508                                                 r.sub.11 = -0.5796                                                                        d.sub.11 = 0.3277                                                                        n.sub.7 = 1.78472                                                                         ν.sub.7 = 25.77                         r.sub.12 = ∞                                                                        d.sub.12 = 0.6881                                                                        n.sub.8 = 1.69680                                                                         ν.sub.8 = 55.52                         r.sub.13 = -1.0103                                                            aspherical coefficient                                                        E = 0.15361, F = 0.49078 × 10.sup.-5, p = 1                             |R.sub.1 | = 0.426, ΔK = 0.075                         ##STR14##                                                                    h.sub.1 /I.sub.max = 0.503, |R.sub.min | = 0.426,           f.sub.2 = 2.036                                                               tan α = 0.1113, tan ω.sub.1 = 0.764                           

    ______________________________________                                        Embodiment 15                                                                 f = 1.000, F/6.712, 2ω = 75.37°                                  IH = 0.6751, object distance = -16.4654                                       ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.2195                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.1098                                                  r.sub.3 = 2.2137                                                              (aspherical surface)                                                                      d.sub.3 = 0.2744                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = 0.4281                                                                          d.sub.4 = 0.2195                                                  r.sub.5 = ∞                                                                         d.sub.5 = 0.7695                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.6 = ∞ (stop)                                                                  d.sub.6 = 2.0845                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = -1.2562                                                                         d.sub.7 = 0.1647                                                  r.sub.8 = 1.9566                                                                          d.sub.8 = 1.0154                                                                         n.sub. 5 = 1.60311                                                                        ν.sub.5 = 60.70                         r.sub.9 = -0.9929                                                                         d.sub.9 = 0.2195                                                                         n.sub.6 = 1.84666                                                                         ν.sub.6 = 23.78                         r.sub.10 = -4.8679                                                                        d.sub.10 = 0.2744                                                 r.sub.11 = -0.8676                                                                        d.sub.11 = 0.3293                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.78                         r.sub.12 = -33.1108                                                                       d.sub.12 = 0.1482                                                 r.sub.13 = 1.8412                                                                         d.sub.13 = 0.5982                                                                        n.sub.8 = 1.65160                                                                         ν.sub.8 = 58.52                         r.sub.14 = -2.9468                                                            aspherical coefficient                                                        E = 0.23287, F = -0.83235 × 10.sup.-2, p = 1                            |R.sub.1 | = 0.4281, ΔK = 0.067                        ##STR15##                                                                    h.sub.1 /I.sub.max = 0.547, |R.sub.min | = 0.4281,          f.sub.2 = 1.535                                                               tan α = 0.2159, tan ω.sub.1 = 0.772                               ______________________________________                                        Embodiment 16                                                                 f = 1.000, F/6.062, 2ω = 93.65°                                  IH = 1.0191, object distance = -24.8550                                       ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.2486                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.1657                                                  r.sub.3 = 3.2886                                                              (aspherical surface)                                                                      d.sub.3 = 0.4143                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = 0.5513                                                                          d.sub.4 = 0.3314                                                  r.sub.5 = ∞                                                                         d.sub.5 = 1.3523                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.6 = ∞ (stop)                                                                  d.sub.6  = 2.9559                                                                        n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = -1.7553                                                                         d.sub.7 = 0.2486                                                  r.sub.8 = 76.0049                                                                         d.sub.8 = 1.2428                                                                         n.sub.5 = 1.60311                                                                         ν.sub.5 = 60.70                         r.sub.9 = -1.1701                                                                         d.sub.9 = 0.3314                                                                         n.sub.6 = 1.84666                                                                         ν.sub.6 = 23.78                         r.sub.10 = -3.0256                                                                        d.sub.10 = 0.6628                                                 r.sub.11 = -10.0965                                                                       d.sub.11 = 0.4971                                                                        n.sub.7 = 1.78472                                                                         ν.sub.7 = 25.68                         r.sub.12 = ∞                                                                        d.sub.12 = 1.0439                                                                        n.sub.8 = 1.69680                                                                         ν.sub.8 = 55.52                         r.sub.13 = -5.9017                                                            aspherical coefficient                                                        E = 0.10046, F = 0.68773 × 10.sup.-6, p = 1                             |R.sub.1 | = 0.5513, ΔK = 0.074                        ##STR16##                                                                    h.sub.1 /I.sub.max = 0.724, |R.sub.min | = 0.5513,          f.sub.2 = 2.266                                                               tan α = 0.3913, tan ω.sub.1 = 1.066                               ______________________________________                                        Embodiment 17                                                                 f = 1.000, F/6.396, 2ω = 68°                                     IH = 0.65, object distance = -8.9659                                          ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.1195                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.0598                                                  r.sub.3 = 7.6111                                                              (aspherical surface)                                                                      d.sub.3 = 0.3885                                                                         n.sub.2 = 1.78472                                                                         ν.sub.2 = 25.71                         r.sub.4 = ∞                                                                         d.sub.4 = 0.1195                                                                         n.sub.3 =  1.58144                                                                        ν.sub.3 = 40.75                         r.sub.5 = 0.3752                                                                          d.sub.5 = 0.2391                                                  r.sub.6 = ∞                                                                         d.sub.6 = 0.7553                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = ∞ (stop)                                                                  d.sub.7 = 2.0420                                                                         n.sub.5 = 1.80610                                                                         ν.sub.5 = 40.95                         r.sub.8 = -1.2914                                                                         d.sub.8 = 0.0897                                                  r.sub.9 = 2.4782                                                                          d.sub.9 = 0.8966                                                                         n.sub.6 = 1.60311                                                                         ν.sub.6 = 60.70                         r.sub.10 = -0.9432                                                                        d.sub.10 = 0.2989                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.88                         r.sub.11 = -4.1375                                                                        d.sub.11 = 0.8458                                                 r.sub.12 = -0.8129                                                                        d.sub.12 = 0.2989                                                                        n.sub.8 = 1.58144                                                                         ν.sub.8 = 40.75                         r.sub.13 = ∞                                                                        d.sub.13 = 0.6874                                                                        n.sub.9 =  1.60311                                                                        ν.sub.9 = 60.70                         r.sub.14 = -1.1904                                                            aspherical coefficient                                                        E = 0.19416, p = 1                                                            |R.sub.1 | = 0.3752, ΔK = 0.032                        ##STR17##                                                                    h.sub.1 /I.sub.max = 1.005, |R.sub.min | = 0.3752,          f.sub.2 = 1.826                                                               tan α = 0.1223, tan ω.sub.1 = 0.675                               ______________________________________                                        Embodiment 18                                                                 f = 1.000, F/6.449, 2ω = 68°                                     IH = 0.65, object distance = -9.0009                                          ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.1200                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 =  0.0600                                                 r.sub.3 = 2.4002                                                              (aspherical surface)                                                                      d.sub.3 = 0.3900                                                                         n.sub.2 = 1.78472                                                                         ν.sub.2 = 25.71                         r.sub.4 = ∞                                                                         d.sub.4 = 0.1200                                                                         n.sub.3 = 1.58144                                                                         ν.sub.3 = 40.75                         r.sub.5 = 0.2856                                                                          d.sub.5 = 0.2400                                                  r.sub.6 = ∞                                                                         d.sub.6 = 0.7583                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = ∞ (stop)                                                                  d.sub.7 = 2.0500                                                                         n.sub.5 = 1.80610                                                                         ν.sub.5 = 40.95                         r.sub.8 = -1.2964                                                                         d.sub.8 = 0.0900                                                  r.sub.9 = 2.4878                                                                          d.sub.9 = 0.9001                                                                         n.sub.6 = 1.60311                                                                         ν.sub.6 = 60.70                         r.sub.10 = -0.9469                                                                        d.sub.10 = 0.3000                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.88                         r.sub.11 = -4.1536                                                                        d.sub.11 = 0.8491                                                 r.sub.12 = -0.8161                                                                        d.sub.12 = 0.3000                                                                        n.sub.8 = 1.58144                                                                         ν.sub.8 = 40.75                         r.sub.13 = ∞                                                                        d.sub.13 = 0.6901                                                                        n.sub.9 = 1.60311                                                                         ν.sub.9 = 60.70                         r.sub.14 = -1.1950                                                            aspherical coefficient                                                        F = 0.45780, p = 1                                                            |R.sub.1 | = 0.2856, ΔK = 0.027                        ##STR18##                                                                    h.sub.1 /I.sub.max = 1.238, |R.sub.min | = 0.2856,          f.sub.2 = 1.833                                                               tan α = 0.1010, tan ω.sub.1 = 0.675                               ______________________________________                                        Embodiment 19                                                                 f = 1.000, F/4.966, 2ω = 69.886°                                 IH = 0.6431, object distance = -8.8496                                        ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.0885                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.0590                                                  r.sub.3 = 4.8865                                                              (aspherical surface)                                                                      d.sub.3 = 0.3835                                                                         n.sub.2 = 1.78472                                                                         ν.sub.2 = 25.71                         r.sub.4 = ∞                                                                         d.sub.4 = 0.1180                                                                         n.sub.3 = 1.58144                                                                         ν.sub.3 = 40.75                         r.sub.5 = 0.3540                                                                          d.sub.5 = 0.2360                                                  r.sub.6 = ∞                                                                         d.sub.6 = 0.7563                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = ∞ (stop)                                                                  d.sub.7 = 2.0048                                                                         n.sub.5 = 1.80610                                                                         ν.sub.5 = 40.95                         r.sub.8 = -1.2746                                                                         d.sub.8 = 0.0885                                                  r.sub.9 = 2.4460                                                                          d.sub.9 = 0.8850                                                                         n.sub. 6 = 1.60311                                                                        ν.sub.6 = 60.70                         r.sub.10 = -0.9310                                                                        d.sub.10 = 0.2950                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.88                         r.sub.11 = -4.0838                                                                        d.sub.11 = 0.8348                                                 r.sub.12 = -0.8024                                                                        d.sub.12 = 0.2950                                                                        n.sub.8 = 1.58144                                                                         ν.sub.8 = 40.75                         r.sub.13 = ∞                                                                        d.sub.13 = 0.6785                                                                        n.sub.9 = 1.60311                                                                         ν.sub.9 = 60.70                         r.sub.14 = -1.1749                                                                        d.sub.14 = 2.0649                                                 r.sub.15 = 5.5838                                                                         d.sub.15 = 12.8909                                                                       n.sub.10 = 1.62004                                                                        ν.sub.10 = 36.25                        r.sub.16 = ∞                                                                        d.sub.16 = 0.7611                                                 r.sub.17 = 4.1673                                                                         d.sub.17 = 0.2950                                                                        n.sub.11 = 1.80610                                                                        ν.sub.11 = 40.95                        r.sub.18 = 1.9038                                                                         d.sub.18 = 0.8850                                                                        n.sub.12 = 1.65160                                                                        ν.sub.12 = 58.52                        r.sub.19 = -7.4569                                                                        d.sub.19 = 0.5310                                                 r.sub.20 = ∞                                                                        d.sub.20 = 12.8909                                                                       n.sub.13 = 1.62004                                                                        ν.sub.13 = 36.25                        r.sub.21 = -5.5838                                                                        d.sub.21 = 2.3599                                                 r.sub.22 = 5.5838                                                                         d.sub.22 = 12.8909                                                                       n.sub.14 = 1.62004                                                                        ν.sub.14 = 36.25                        r.sub.23 = ∞                                                                        d.sub.23 = 0.7611                                                 r.sub.24 = 4.1673                                                                         d.sub.24 = 0.2950                                                                        n.sub.15 = 1.80610                                                                        ν.sub.15 = 40.95                        r.sub.25 = 1.9038                                                                         d.sub.25 = 0.8850                                                                        n.sub.16 = 1.65160                                                                        ν.sub.16 = 58.52                        r.sub.26 = -7.4569                                                                        d.sub.26 = 0.5310                                                 r.sub.27 = ∞                                                                        d.sub.27 = 12.8909                                                                       n.sub.17 = 1.62004                                                                        ν.sub.17 = 36.25                        r.sub.28 = -5.5838                                                                        d.sub.28 = 2.3599                                                 r.sub.29 = 5.5838                                                                         d.sub.29 = 12.8909                                                                       n.sub.18 = 1.62004                                                                        ν.sub.18 = 36.25                        r.sub.30 = ∞                                                                        d.sub.30 = 0.7611                                                 r.sub.31 = 4.1673                                                                         d.sub.31 = 0.2950                                                                        n.sub.19 = 1.80610                                                                        ν.sub.19 = 40.95                        r.sub.32 = 1.9038                                                                         d.sub.32 = 0.8850                                                                        n.sub.20 = 1.65160                                                                        ν.sub.20 = 58.52                        r.sub.33 = -7.4569                                                                        d.sub.33 = 0.5310                                                 r.sub.34 = ∞                                                                        d.sub.34 = 12.8909                                                                       n.sub.21 = 1.62004                                                                        ν.sub.21 = 36.25                        r.sub.35 = -4.1673                                                            ______________________________________                                        Embodiment 20                                                                 f = 1.000, F/6.385, 2ω = 70.314°                                 IH = 0.7089                                                                   ______________________________________                                        r.sub.1 = ∞                                                                         d.sub.1 = 0.2305                                                                         n.sub.1 = 1.76900                                                                         ν.sub.1 = 64.15                         r.sub.2 = ∞                                                                         d.sub.2 = 0.1153                                                  r.sub.3 = 2.1028                                                              (aspherical surface)                                                                      d.sub.3 = 0.2882                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = 0.4496                                                                          d.sub.4 = 0.2305                                                  r.sub.5 = ∞                                                                         d.sub.5 = 0.7927                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.6 = ∞ (stop)                                                                  d.sub.6 = 2.2045                                                                         n.sub.4 = 1.80610                                                                         ν.sub.4 = 40.95                         r.sub.7 = -1.2922                                                                         d.sub.7 = 0.1729                                                  r.sub.8 = 2.8519                                                                          d.sub.8 = 1.0663                                                                         n.sub.5 = 1.60311                                                                         ν.sub.5 = 60.70                         r.sub.9 = -1.0767                                                                         d.sub.9 = 0.2305                                                                         n.sub.6 = 1.84666                                                                         ν.sub.6 = 23.78                         r.sub.10 = -3.0726                                                                        d.sub.10 = 0.2882                                                 r.sub.11  = -0.9798                                                                       d.sub.11 = 0.3458                                                                        n.sub.7 = 1.84666                                                                         ν.sub.7 = 23.78                         r.sub.12 = -9.2888                                                                        d.sub.12 = 0.1556                                                 r.sub.13 = 2.6974                                                                         d.sub.13 = 0.6282                                                                        n.sub.8 = 1.65160                                                                         ν.sub.8 = 58.67                         r.sub.14 = -2.6974                                                                        d.sub.14 = 2.5533                                                 r.sub.15 = 6.8830                                                                         d.sub.15 = 14.9914                                                                       n.sub.9 = 1.62004                                                                         ν.sub.9 = 36.25                         r.sub.16 = ∞                                                                        d.sub.16 = 1.4525                                                 r.sub.17 = 4.6340                                                                         d.sub.17 = 0.9280                                                                        n.sub.10 = 1.80610                                                                        ν.sub.10 = 40.95                        r.sub.18 = 2.0749                                                                         d.sub.18 = 1.5447                                                                        n.sub.11 = 1.65160                                                                        ν.sub.11 = 58.67                        r.sub.19 = -9.4871                                                                        d.sub.19 = 0.6801                                                 r.sub.20 = ∞                                                                        d.sub.20 = 14.9914                                                                       n.sub.12  = 1.62004                                                                       ν.sub.12 = 36.25                        r.sub.21 = -6.8830                                                                        d.sub.21 = 2.3055                                                 r.sub.22 = 6.8830                                                                         d.sub.22 = 14.9914                                                                       n.sub.13 = 1.62004                                                                        ν.sub.13 = 36.25                        r.sub.23 = ∞                                                                        d.sub.23 = 1.4525                                                 r.sub.24 = 4.6340                                                                         d.sub.24 = 0.9280                                                                        n.sub.14 = 1.80610                                                                        ν.sub.14 = 40.95                        r.sub.25 = 2.0749                                                                         d.sub.25 = 1.5447                                                                        n.sub.15 = 1.65160                                                                        ν.sub.15 = 58.67                        r.sub.26 = -9.4871                                                                        d.sub.26 = 0.6801                                                 r.sub.27 = ∞                                                                        d.sub.27 = 14.9914                                                                       n.sub.16 = 1.62004                                                                        ν.sub.16 = 36.25                        r.sub.28 = -6.8830                                                                        d.sub.28 = 2.3055                                                 r.sub.29 = 6.8830                                                                         d.sub.29 = 14.9914                                                                       n.sub.17 = 1.62004                                                                        ν.sub.17 = 36.25                        r.sub.30  = ∞                                                                       d.sub.30 = 1.4525                                                 r.sub.31 = 4.6340                                                                         d.sub.31 = 0.9280                                                                        n.sub.18 = 1.80610                                                                        ν.sub.18 = 40.95                        r.sub.32 = 2.0749                                                                         d.sub.32 = 1.5447                                                                        n.sub.19 = 1.65160                                                                        ν.sub.19 = 58.67                        r.sub.33 = -9.4871                                                                        d.sub.33 = 0.6801                                                 r.sub.34 = ∞                                                                        d.sub.34 = 14.9914                                                                       n.sub.20 = 1.62004                                                                        ν.sub.20 = 36.25                        r.sub.35 = -6.8830                                                                        d.sub.35 = 2.3055                                                 r.sub.36 = 6.8830                                                                         d.sub.36 = 14.9914                                                                       n.sub.21 = 1.62004                                                                        ν.sub.21 = 36.25                        r.sub.37 = ∞                                                                        d.sub.37 = 1.4525                                                 r.sub.38 = 4.6340                                                                         d.sub.38 = 0.9280                                                                        n.sub.22 = 1.80610                                                                        ν.sub.22 = 40.95                        r.sub.39 = 2.0749                                                                         d.sub.39 = 1.5447                                                                        n.sub.23  = 1.65160                                                                       ν.sub.23 = 58.67                        r.sub.40 = -9.4871                                                                        d.sub.40 = 0.6801                                                 r.sub.41 = ∞                                                                        d.sub.41 = 14.9914                                                                       n.sub.24 = 1.62004                                                                        ν.sub.24 = 36.25                        r.sub.42 = -6.8830                                                                        d.sub.42 = 2.3055                                                 r.sub.43 = 6.8830                                                                         d.sub.43 = 14.9914                                                                       n.sub.25 = 1.62004                                                                        ν.sub.25 = 36.25                        r.sub.44 = ∞                                                                        d.sub.44 = 1.4525                                                 r.sub.45 = 4.6340                                                                         d.sub.45 = 0.9280                                                                        n.sub.26 = 1.80610                                                                        ν.sub.26 = 40.95                        r.sub.46 = 2.0749                                                                         d.sub.46 = 1.5447                                                                        n.sub.27 = 1.65160                                                                        ν.sub.27 = 58.67                        r.sub.47 = -9.4871                                                                        d.sub.47 = 0.6801                                                 r.sub.48 = ∞                                                                        d.sub.48 = 14.4150                                                                       n.sub.28 = 1.62004                                                                        ν.sub.28 = 36.25                        r.sub.49 =  ∞                                                                       d.sub.49 = 0.5764                                                                        n.sub.29 = 1.62004                                                                        ν.sub.29 = 36.25                        r.sub.50 = -18.2640                                                           ______________________________________                                        Embodiment 21                                                                 f = 4.330, F/5.69, 2ω = 80.4°                                    IH = 1.712, object distance = 50                                              ______________________________________                                        r.sub.1 = 7.5850                                                              (aspherical surface)                                                                      d.sub.1 = 1.0000                                                                         n.sub.1 = 1.78471                                                                         ν.sub.1 = 25.71                         r.sub.2 = 1.9040                                                                          d.sub.2 = 1.2000                                                  r.sub.3 = ∞                                                                         d.sub.3 = 6.7000                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = ∞                                                                         d.sub.4 = 8.0000                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.5 = -7.1300                                                                         d.sub.5 = 2.0000                                                  r.sub.6 = 9.1560                                                                          d.sub.6 = 5.0000                                                                         n.sub.4 = 1.51633                                                                         ν.sub.4 = 64.15                         r.sub.7 =  -6.0310                                                                        d.sub.7 = 1.5000                                                                         n.sub.5 = 1.84666                                                                         ν.sub.5 = 23.78                         r.sub.8 = -95.7310                                                                        d.sub.8 = 3.0000                                                  r.sub.9 = 29.4330                                                                         d.sub.9 = 5.0000                                                                         n.sub.6 = 1.51633                                                                         ν.sub.6 = 64.15                         r.sub.10 = ∞                                                                        d.sub.10 = 13.0000                                                                       n.sub.7 = 1.51633                                                                         ν.sub.7 = 64.15                         r.sub.11 = -40.9980                                                                       d.sub.11 = 44.0000                                                r.sub.12 = 37.6000                                                                        d.sub.12 = 4.5110                                                                        n.sub.8 = 1.51009                                                                         ν.sub.8 = 63.46                         r.sub.13 = -14.9830                                                                       d.sub.13 = 2.0000                                                                        n.sub.9 = 1.74950                                                                         ν.sub.9 = 35.27                         r.sub.14 = -33.7510                                                                       d.sub.14 = 25.6200                                                r.sub.15 = ∞ (stop)                                                                 d.sub.15 = 25.6200                                                r.sub.16 = 33.7510                                                                        d.sub.16 = 2.0000                                                                        n.sub. 10 = 1.74950                                                                       ν.sub.10 = 35.27                        r.sub.17 = 14.9830                                                                        d.sub.17 = 4.5110                                                                        n.sub.11 = 1.51009                                                                        ν.sub.11 = 63.46                        r.sub.18 = -37.6000                                                                       d.sub.18 = 40.9500                                                r.sub.19 = 55.0600                                                                        d.sub.19 = 22.3000                                                                       n.sub.12 = 1.51633                                                                        ν.sub.12 = 64.15                        r.sub.20 = -55.0600                                                                       d.sub.20 = 40.9500                                                r.sub.21 = 37.6000                                                                        d.sub.21 = 4.5110                                                                        n.sub.13 = 1.51009                                                                        ν.sub.13 = 63.46                        r.sub.22 = -14.9830                                                                       d.sub.22 = 2.0000                                                                        n.sub.14 = 1.74950                                                                        ν.sub.14 = 35.27                        r.sub.23 = -33.7510                                                                       d.sub.23 = 51.2400                                                r.sub.24 = 33.7510                                                                        d.sub.24 = 2.0000                                                                        n.sub.15 = 1.74950                                                                        ν.sub.15 = 35.27                        r.sub.25 = 14.9830                                                                        d.sub.25 = 4.5110                                                                        n.sub.16  = 1.51009                                                                       ν.sub.16 = 63.46                        r.sub.26 = -37.6000                                                                       d.sub.26 = 72.9351                                                r.sub.27 = 57.4060                                                                        d.sub.27 = 1.0000                                                                        n.sub.17 = 1.80518                                                                        ν.sub.17 = 25.43                        r.sub.28 = 16.3250                                                                        d.sub.28 = 4.5000                                                                        n.sub.18 = 1.66998                                                                        ν.sub.18 = 39.27                        r.sub.29 = -21.9620                                                           aspherical coefficient                                                        P = -7.0000, E = 0.62003 × 10.sup.-2                                    F = -0.77437 × 10.sup.-4                                                 ##STR19##                                                                    |cos ω.sub.I - cos ω.sub.0.5 | = 0.158          h.sub.1 /I.sub.max = 0.493, f.sub.2 /f = 1.664                                |R.sub.min |/f = 0.439, tan α = 0.3115,               tan ω.sub. 1 = 0.846, d/I.sub.max = 4.58                                ______________________________________                                        Embodiment 22                                                                 f = 4.330, F/5.69, 2ω = 80.2°                                    IH = 1.708, object distance = 50                                              ______________________________________                                        r.sub.1 = 7.5850                                                              (aspherical surface)                                                                      d.sub.1 = 1.0000                                                                         n.sub.1 = 1.78471                                                                         ν.sub.1 = 25.71                         r.sub.2 = 1.9040                                                                          d.sub.2 = 1.2000                                                  r.sub.3 = ∞                                                                         d.sub.3 = 6.7000                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = ∞                                                                         d.sub.4 = 8.0000                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.5 = -7.1302                                                                         d.sub.5 = 2.0000                                                  r.sub.6 = 9.1562                                                                          d.sub.6 = 5.0000                                                                         n.sub.4 = 1.51633                                                                         ν.sub.4 = 64.15                         r.sub.7 = -6.0314                                                                         d.sub.7 = 1.5000                                                                         n.sub.5  = 1.84666                                                                        ν.sub.5 = 23.78                         r.sub.8 = -95.7314                                                                        d.sub.8 = 3.0000                                                  r.sub.9 = 29.4333                                                                         d.sub.9 = 5.0000                                                                         n.sub.6 = 1.51680                                                                         ν.sub.6 = 64.14                         r.sub.10 = ∞                                                                        d.sub.10 = 13.0000                                                                       n.sub.7 = 1.51680                                                                         ν.sub.7 = 64.14                         r.sub.11 = -40.9983                                                                       d.sub.11 = 44.0005                                                r.sub.12 = 36.5571                                                                        d.sub.12 = 4.5110                                                                        n.sub.8 = 1.50657                                                                         ν.sub.8 = 61.94                         r.sub.13 = -14.7648                                                                       d.sub.13 = 2.0000                                                                        n.sub.9 = 1.74950                                                                         ν.sub.9 = 35.27                         r.sub.14 = -33.5416                                                                       d.sub.14 = 25.6200                                                r.sub.15 = ∞ (stop)                                                                 d.sub.15 = 25.6200                                                r.sub.16 = 33.5416                                                                        d.sub.16 = 2.0000                                                                        n.sub.10 = 1.74950                                                                        ν.sub.10 = 35.27                        r.sub.17 = 14.7648                                                                        d.sub.17 = 4.5110                                                                        n.sub.11  = 1.50657                                                                       ν.sub.11 = 61.94                        r.sub.18 = -36.5571                                                                       d.sub.18 = 40.9500                                                r.sub.19 = 54.9614                                                                        d.sub.19 = 22.3000                                                                       n.sub.12 = 1.51680                                                                        ν.sub.12 = 64.14                        r.sub.20 = -54.9614                                                                       d.sub.20 = 40.9500                                                r.sub.21 = 36.5571                                                                        d.sub.21 = 4.5110                                                                        n.sub.13 = 1.50657                                                                        ν.sub.13 = 61.94                        r.sub.22 = -14.7648                                                                       d.sub.22 = 2.0000                                                                        n.sub.14 = 1.74950                                                                        ν.sub.14 = 35.27                        r.sub.23 = -33.5416                                                                       d.sub.23 = 51.2400                                                r.sub.24 = 33.5416                                                                        d.sub.24 = 2.0000                                                                        n.sub.15 = 1.74950                                                                        ν.sub.15 = 35.27                        r.sub.25 = 14.7648                                                                        d.sub.25 = 4.5110                                                                        n.sub.16 = 1.50657                                                                        ν.sub.16 = 61.94                        r.sub.26 = -36.5571                                                                       d.sub.26 = 73.4215                                                r.sub.27  = 57.4059                                                                       d.sub.27 = 1.0000                                                                        n.sub.17 = 1.80518                                                                        ν.sub.17 = 25.43                        r.sub.28 = 16.3253                                                                        d.sub.28 = 4.5000                                                                        n.sub.18 = 1.66998                                                                        ν.sub.18 = 39.27                        r.sub.29 = -21.9615                                                           aspherical coefficient                                                        P = -7.0000, E = 0.62003 × 10.sup.-2                                    F = -0.77437 × 10.sup.-4                                                 ##STR20##                                                                    |cos ω.sub.1 - cos ω.sub.0.5 | = 0.157          h.sub.1 /I.sub.max = 0.494, f.sub.2 /f = 1.664                                R.sub.min /f = 0.439, tan α = 0.3103                                    tan ω.sub.1 = 0.842, d/I.sub.max = 4.60                                 ______________________________________                                        Embodiment 23                                                                 f = 4.330, F/5.69, 2ω = 81.80°                                   IH =  1.742, object distance = 50                                             ______________________________________                                        r.sub.1 = 7.5850                                                              (aspherical surface)                                                                      d.sub.1 = 1.0000                                                                         n.sub.1 = 1.78471                                                                         ν.sub.1 = 25.71                         r.sub.2 = 1.9040                                                                          d.sub.2 = 1.2000                                                  r.sub.3 = ∞                                                                         d.sub.3 = 6.7000                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = ∞                                                                         d.sub.4 = 8.0000                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.5 = -7.1302                                                                         d.sub.5 = 2.0000                                                  r.sub.6 = 9.1562                                                                          d.sub.6 = 5.0000                                                                         n.sub.4 = 1.51633                                                                         ν.sub.4 = 64.15                         r.sub.7 = -6.0314                                                                         d.sub.7 = 1.5000                                                                         n.sub.5 = 1.84666                                                                         ν.sub.5 = 23.78                         r.sub.8 = -95.7314                                                                        d.sub.8 = 3.0000                                                  r.sub.9 = 29.4333                                                                         d.sub. 9 = 5.0000                                                                        n.sub.6 = 1.51680                                                                         ν.sub.6 = 64.14                         r.sub.10 = ∞                                                                        d.sub.10 = 13.0000                                                                       n.sub.7 = 1.51680                                                                         ν.sub.7 = 64.14                         r.sub.11 = -40.9983                                                                       d.sub.11 = 44.0005                                                r.sub.12 = 38.1046                                                                        d.sub.12 = 4.5110                                                                        n.sub.8 = 1.51633                                                                         ν.sub.8 = 64.15                         r.sub.13 = -14.7435                                                                       d.sub.13 = 2.0000                                                                        n.sub.9 = 1.74950                                                                         ν.sub.9 = 35.27                         r.sub.14 = -34.0380                                                                       d.sub.14 = 25.6200                                                r.sub.15 = ∞ (stop)                                                                 d.sub.15 = 25.6200                                                r.sub.16 = 34.0380                                                                        d.sub.16 = 2.0000                                                                        n.sub.10 = 1.74950                                                                        ν.sub.10 = 35.27                        r.sub.17 = 14.7435                                                                        d.sub.17 = 4.5110                                                                        n.sub.11 = 1.51633                                                                        ν.sub.11 = 64.15                        r.sub.18 = -38.1046                                                                       d.sub.18 = 40.9500                                                r.sub.19 = 54.8163                                                                        d.sub.19 = 22.3000                                                                       n.sub.12 = 1.51680                                                                        ν.sub.12 = 64.14                        r.sub.20 = -54.8163                                                                       d.sub.20 = 40.9500                                                r.sub.21 = 38.1046                                                                        d.sub.21 = 4.5110                                                                        n.sub.13 = 1.51633                                                                        ν.sub.13 = 64.15                        r.sub.22 = -14.7435                                                                       d.sub.22 = 2.0000                                                                        n.sub.14 = 1.74950                                                                        ν.sub.14 = 35.27                        r.sub.23 = -34.0380                                                                       d.sub.23 = 51.2400                                                r.sub.24 = 34.0380                                                                        d.sub.24 = 2.0000                                                                        n.sub.15 = 1.74950                                                                        ν.sub.15 = 35.27                        r.sub.25 = 14.7435                                                                        d.sub.25 = 4.5110                                                                        n.sub.16 = 1.51633                                                                        ν.sub.16 = 64.15                        r.sub.26 = -38.1046                                                                       d.sub.26 = 74.1754                                                r.sub.27 = 545508                                                                         d.sub.27 = 1.0000                                                                        n.sub.17 = 1.80518                                                                        ν .sub.17 = 25.43                       r.sub.28 = 16.8816                                                                        d.sub.28 = 4.5000                                                                        n.sub.18 = 1.65128                                                                        ν.sub.18 = 38.25                        r.sub.29 = -22.0046                                                           aspherical coefficient                                                        P = -7.0000, E = 0.62003 × 10.sup.-2                                    F = -0.77437 × 10.sup.-4                                                 ##STR21##                                                                    |cos ω.sub.I - cos ω.sub.0.5 | = 0.162          h.sub.1 /I.sub.max = 0.491, f.sub.2 /f = 1.664                                |R.sub.min |/f = 0.439, tan α = 0.3200                tan ω.sub.1 = 0.866, d/I.sub.max = 4.48                                 ______________________________________                                        Embodiment 24                                                                 f = 4.330, F/5.69, 2ω = 80.0°                                    IH = 1.700, object distance = 50                                              ______________________________________                                        r.sub.1 =  7.5850                                                             (aspherical surface)                                                                      d.sub.1 = 1.0000                                                                         n.sub.1 = 1.78471                                                                         ν.sub.1 = 25.71                         r.sub.2 = 1.9040                                                                          d.sub.2 = 1.2000                                                  r.sub.3 = ∞                                                                         d.sub.3 = 6.7000                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = ∞                                                                         d.sub.4 = 8.0000                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.5 = -7.1302                                                                         d.sub.5 = 2.0000                                                  r.sub.6 = 9.1562                                                                          d.sub.6 = 5.0000                                                                         n.sub.4 = 1.51633                                                                         ν.sub.4 = 64.15                         r.sub.7 = -6.0314                                                                         d.sub.7 = 1.5000                                                                         n.sub.5 = 1.84666                                                                         ν.sub.5 = 23.78                         r.sub.8 = -95.7314                                                                        d.sub.8 = 3.0000                                                  r.sub.9 = 29.4333                                                                         d.sub.9 = 5.0000                                                                         n.sub.6 = 1.51680                                                                         ν.sub.6  = 64.14                        r.sub.10 = ∞                                                                        d.sub.10 = 13.0000                                                                       n.sub.7 = 1.51680                                                                         ν.sub.7 = 64.14                         r.sub.11 = -40.9983                                                                       d.sub.11 = 44.0005                                                r.sub.12 = 42.4824                                                                        d.sub.12 = 4.5110                                                                        n.sub.8 = 1.51633                                                                         ν.sub.8 = 64.15                         r.sub.13 = -15.1077                                                                       d.sub.13 = 2.0000                                                                        n.sub.9 = 1.74950                                                                         ν.sub.9 = 35.27                         r.sub.14 = -32.6979                                                                       d.sub.14 = 25.6200                                                r.sub.15 = ∞ (stop)                                                                 d.sub.15 = 25.6200                                                r.sub.16 = 32.6979                                                                        d.sub.16 = 2.0000                                                                        n.sub.10 = 1.74950                                                                        ν.sub.10 = 35.27                        r.sub.17 = 15.1077                                                                        d.sub.17 = 4.5110                                                                        n.sub.11 = 1.51633                                                                        ν.sub.11 = 64.15                        r.sub.18 = -42.4824                                                                       d.sub.18 = 40.9500                                                r.sub.19 = 53.3038                                                                        d.sub. 19 = 22.3000                                                                      n.sub.12 = 1.51680                                                                        ν.sub.12 = 64.14                        r.sub.20 = -53.3038                                                                       d.sub.20 = 40.9500                                                r.sub.21 = 42.4824                                                                        d.sub.21 = 4.5110                                                                        n.sub.13 = 1.51633                                                                        ν.sub.13 = 64.15                        r.sub.22 = -15.1077                                                                       d.sub.22 = 2.0000                                                                        n.sub.14 = 1.74950                                                                        ν.sub.14 = 35.27                        r.sub.23 = -32.6979                                                                       d.sub.23 = 51.2400                                                r.sub.24 = 32.6979                                                                        d.sub.24 = 2.0000                                                                        n.sub.15 = 1.74950                                                                        ν.sub.15 = 35.27                        r.sub.25 = 15.1077                                                                        d.sub.25 = 4.5110                                                                        n.sub.16 = 1.51633                                                                        ν.sub.16 = 64.15                        r.sub.26 = -42.4824                                                                       d.sub.26 = 73.3230                                                r.sub.27 = 50.5778                                                                        d.sub.27 = 1.0000                                                                        n.sub.17 = 1.80518                                                                        ν.sub.17 = 25.43                        r.sub.28 = 15.8191                                                                        d.sub. 28 = 4.5000                                                                       n.sub.18 = 1.65128                                                                        ν.sub.18 = 38.25                        r.sub.29 = -21.6085                                                           aspherical coefficient                                                        P = -7.0000, E = 0.62003 × 10.sup.-2                                    F = -0.77437 × 10.sup.-4                                                 ##STR22##                                                                    |cos ω.sub.I - cos ω.sub.0.5 | = 0.157          h.sub.1 /I.sub.max = 0.494, f.sub.2 /f = 1.664                                |R.sub.min |/f = 0.439, tan α = 0.3080                tan ω.sub.1 = 0.839, d/I.sub.max = 4.62                             

    ______________________________________                                        Embodiment 25                                                                 f = 4.093, F/5.69, 2ω = 79.9°                                    IH = 2.603, object distance = 50                                              ______________________________________                                        r.sub.1 = 20.4600                                                             (aspherical surface)                                                                      d.sub.1 = 1.0000                                                                         n.sub.1 = 1.78471                                                                         ν.sub.1 = 25.71                         r.sub.2 = 2.7218                                                                          d.sub.2 = 1.2000                                                  r.sub.3 = ∞                                                                         d.sub.3 = 15.0000                                                                        n.sub.2 = 1.78800                                                                         ν.sub.2 = 47.38                         r.sub.4 = -7.6691                                                                         d.sub.4 = 0.2003                                                  r.sub.5 = 24.2126                                                                         d.sub.5 = 4.5000                                                                         n.sub.3 = 1.60311                                                                         ν.sub.3 = 60.70                         r.sub.6 = -5.000                                                                          d.sub.6 = 1.4830                                                                         n.sub.4 = 1.84666                                                                         ν.sub.4 = 23.78                         r.sub.7 = -18.6930                                                                        d.sub.7 = 5.6100                                                  r.sub.8 = 12.2983                                                                         d.sub.8 = 5.0000                                                                         n.sub.5 =  1.51680                                                                        ν.sub.5 = 64.14                         r.sub.9 = ∞                                                                         d.sub.9 = 13.0000                                                                        n.sub.6 = 1.51680                                                                         ν.sub.6 = 64.14                         r.sub.10 = -29.0938                                                                       d.sub.10 = 43.9999                                                r.sub.11 = 69.2137                                                                        d.sub.11 = 4.5110                                                                        n.sub.7 = 1.51680                                                                         ν.sub.7 = 64.14                         r.sub.12 = -14.3232                                                                       d.sub.12 = 2.0000                                                                        n.sub.8 = 1.66446                                                                         ν.sub.8 = 35.81                         r.sub.13 = -29.8775                                                                       d.sub.13 = 25.6200                                                r.sub.14 = ∞ (stop)                                                                 d.sub.14 = 25.6200                                                r.sub.15 = 29.8750                                                                        d.sub.15 = 2.0000                                                                        n.sub.9 = 1.66446                                                                         ν.sub.9 = 35.81                         r.sub.16 = 14.3232                                                                        d.sub.16 = 4.5110                                                                        n.sub.10 = 1.51680                                                                        ν.sub.10 = 64.14                        r.sub.17 = -69.2137                                                                       d.sub.17 = 40.9500                                                r.sub.18 = 59.9772                                                                        d.sub.18 = 22.3000                                                                       n.sub.11 = 1.51680                                                                        ν.sub.11 = 64.14                        r.sub.19 = -59.9772                                                                       d.sub.19 = 40.9500                                                r.sub.20 = 69.2137                                                                        d.sub.20 = 4.5110                                                                        n.sub.12 = 1.51680                                                                        ν.sub.12 = 64.14                        r.sub.21 = -14.3232                                                                       d.sub.21 = 2.0000                                                                        n.sub.13 = 1.66446                                                                        ν.sub.13 = 35.81                        r.sub.22 = -29.8775                                                                       d.sub.22 = 51.2400                                                r.sub.23 = 29.8750                                                                        d.sub.23 = 2.0000                                                                        n.sub.14 = 1.66446                                                                        ν.sub.14 = 35.81                        r.sub.24 = 14.3232                                                                        d.sub.24 = 4.5110                                                                        n.sub.15 = 1.51680                                                                        ν.sub.15 = 64.14                        r.sub.25 = -69.2137                                                                       d.sub.25 = 73.5603                                                r.sub.26 = 108.6187                                                                       d.sub.26 = 1.9869                                                                        n.sub.16 = 1.78472                                                                        ν.sub.16 = 25.71                        r.sub.27  = 16.4237                                                                       d.sub.27 = 4.5000                                                                        n.sub.17 = 1.66998                                                                        ν.sub.17 = 39.27                        r.sub.28 = -19.3120                                                           aspherical coefficient                                                        P = -33.9147, E = 0.38319 × 10.sup.-2                                   F = -0.77360 × 10.sup.-4, G = 0.14079 × 10.sup.-8                 L = -0.87328 × 10.sup.-28                                                ##STR23##                                                                    |cos ω.sub.I - cos ω.sub.0.5 | = 0.150          h.sub.1 /I.sub.max = 0.761, f.sub.2 /f = 2.111                                |R.sub.min |/f = 0.665, tan α = 0.3170,               tan ω.sub.1 = 0.838, d/I.sub.max = 4.74                                 ______________________________________                                        Embodiment 26                                                                 f = 4.449, F/5.88, 2ω = 79.6°                                    IH = 1.699, object distance =  50                                             ______________________________________                                        r.sub.1 = 6.3185                                                              (aspherical surface)                                                                      d.sub.1 = 1.0000                                                                         n.sub.1 = 1.78471                                                                         ν.sub.1 = 25.71                         r.sub.2 = 1.9000                                                                          d.sub.2 = 0.9000                                                  r.sub.3 = ∞                                                                         d.sub.3 = 6.7000                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = ∞                                                                         d.sub.4 = 8.2000                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.5 = -7.0109                                                                         d.sub.5 = 2.0000                                                  r.sub.6 = 11.8936                                                                         d.sub.6 = 5.0000                                                                         n.sub.4 = 1.51633                                                                         ν.sub.4 = 64.15                         r.sub.7 = -5.7154                                                                         d.sub.7 = 1.5000                                                                         n.sub.5 = 1.84666                                                                         ν.sub.5 = 23.78                         r.sub.8 = -28.9737                                                                        d.sub.8 = 3.0000                                                  r.sub.9 = 21.4710                                                                         d.sub.9 = 5.0000                                                                         n.sub.6 = 1.51680                                                                         ν.sub.6 = 64.14                         r.sub.10 = ∞                                                                        d.sub.10 = 13.0000                                                                       n.sub.7 = 1.51680                                                                         ν.sub.7 = 64.14                         r.sub.11 = -98.0103                                                                       d.sub.11 = 44.0004                                                r.sub.12 = 42.4824                                                                        d.sub.12 = 4.5110                                                                        n.sub.8 = 1.51633                                                                         ν.sub.8 = 64.15                         r.sub.13 = -15.1077                                                                       d.sub.13 = 2.0000                                                                        n.sub.9 = 1.74950                                                                         ν.sub.9 = 35.27                         r.sub.14 = -32.6979                                                                       d.sub.14 = 25.6200                                                r.sub.15 = ∞ (stop)                                                                 d.sub.15 = 25.6200                                                r.sub.16 = 32.6979                                                                        d.sub.16 = 2.0000                                                                        n.sub.10 = 1.74950                                                                        ν.sub.10 = 35.27                        r.sub.17 = 15.1077                                                                        d.sub.17 = 4.5110                                                                        n.sub.11 = 1.51633                                                                        ν.sub.11 = 64.15                        r.sub.18 = -42.4824                                                                       d.sub.18 = 40.9500                                                r.sub.19 = 53.3038                                                                        d.sub.19 = 22.3000                                                                       n.sub.12 = 1.51680                                                                        ν.sub.12 = 64.14                        r.sub.20 = -53.3038                                                                       d.sub.20 = 40.9500                                                r.sub.21 = 42.4824                                                                        d.sub.21 = 4.5110                                                                        n.sub.13 = 1.51633                                                                        ν.sub.13 = 64.15                        r.sub.22 = -15.1077                                                                       d.sub.22 = 2.0000                                                                        n.sub.14 = 1.74950                                                                        ν.sub.14 = 35.27                        r.sub.23 = -32.6979                                                                       d.sub.23 = 51.2400                                                r.sub.24 = 32.6979                                                                        d.sub.24 = 2.0000                                                                        n.sub.15 = 1.74950                                                                        ν.sub.15 = 35.27                        r.sub.25 = 15.1077                                                                        d.sub.25 = 4.5110                                                                        n.sub.16 = 1.51633                                                                        ν.sub.16 = 64.15                        r.sub.26 = -42.4824                                                                       d.sub.26 = 73.8245                                                r.sub.27 = 50.5778                                                                        d.sub.27 = 1.0000                                                                        n.sub.17 = 1.80518                                                                        ν.sub.17 = 25.43                        r.sub. 28 = 15.8191                                                                       d.sub.28 = 4.5000                                                                        n.sub.18 = 1.65128                                                                        ν.sub.18 = 38.25                        r.sub.29 = -21.6085                                                           aspherical coefficient                                                        P = -10.0000, E = 0.70425 × 10.sup.-2                                   F = -0.77432 × 10.sup.-4, G = 0.14068 × 10.sup.-8                 L = -0.87328 × 10.sup.-28                                                ##STR24##                                                                    |cos ω.sub.I - cos ω.sub.0.5 | = 0.154          h.sub.1 /I.sub.max = 0.477, f.sub.2 /f = 1.709                                |R.sub.min |/f = 0.427, tan α = 0.3365                tan ω.sub.1 = 0.834, d/I.sub.max = 4.44                                 ______________________________________                                        Embodiment 27                                                                 f = 4.449, F/5.88, 2ω = 79.6°                                    IH = 1.699,  object distance = 50                                             ______________________________________                                        r.sub.1 = 6.3185                                                              (aspherical surface)                                                                      d.sub.1 = 1.0000                                                                         n.sub.1  = 1.78471                                                                        ν.sub.1 = 25.71                         r.sub.2 = 1.9000                                                                          d.sub.2 = 0.9000                                                  r.sub.3 = ∞                                                                         d.sub.3 = 6.7000                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = ∞                                                                         d.sub.4 = 8.2000                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.5 = -7.0109                                                                         d.sub.5 = 2.0000                                                  r.sub.6 = 11.8936                                                                         d.sub.6 = 5.0000                                                                         n.sub.4 = 1.51633                                                                         ν.sub.4 = 64.15                         r.sub.7 = -5.7154                                                                         d.sub.7 = 1.5000                                                                         n.sub.5 = 1.84666                                                                         ν.sub.5 = 23.78                         r.sub.8 = -28.9737                                                                        d.sub.8 = 3.0000                                                  r.sub.9 = 21.4710                                                                         d.sub.9 = 5.0000                                                                         n.sub. 6 = 1.51680                                                                        ν.sub.6 = 64.14                         r.sub.10 = ∞                                                                        d.sub.10 = 13.0000                                                                       n.sub.7 = 1.51680                                                                         ν.sub.7 = 64.14                         r.sub.11 = -98.0103                                                                       d.sub.11 = 44.0004                                                r.sub.12 = 42.4824                                                                        d.sub.12 = 4.5110                                                                        n.sub.8 = 1.51633                                                                         ν.sub.8 = 64.15                         r.sub.13 = -15.1077                                                                       d.sub.13 = 2.0000                                                                        n.sub.9 = 1.74950                                                                         ν.sub.9 = 35.27                         r.sub.14 = -32.6979                                                                       d.sub.14 = 25.6200                                                r.sub.15 = ∞ (stop)                                                                 d.sub.15 = 25.6200                                                r.sub.16 = 32.6979                                                                        d.sub.16 = 2.0000                                                                        n.sub.10 = 1.74950                                                                        ν.sub.10 = 35.27                        r.sub.17 = 15.1077                                                                        d.sub.17 = 4.5110                                                                        n.sub.11 = 1.51633                                                                        ν.sub.11 = 64.15                        r.sub.18 = -42.4824                                                                       d.sub.18 =  40.9500                                               r.sub.19 = 53.3038                                                                        d.sub.19 = 22.3000                                                                       n.sub.12 = 1.51680                                                                        ν.sub.12 = 64.14                        r.sub.20 = -53.3038                                                                       d.sub.20 = 40.9500                                                r.sub.21 = 42.4824                                                                        d.sub.21 = 4.5110                                                                        n.sub.13 = 1.51633                                                                        ν.sub.13 = 64.15                        r.sub.22 = -15.1077                                                                       d.sub.22 = 2.0000                                                                        n.sub.14 = 1.74950                                                                        ν.sub.14 = 35.27                        r.sub.23 = -32.6979                                                                       d.sub.23 = 51.2400                                                r.sub.24 = 32.6979                                                                        d.sub.24 = 2.0000                                                                        n.sub.15 = 1.74950                                                                        ν.sub.15 = 35.27                        r.sub.25 = 15.1077                                                                        d.sub.25 = 4.5110                                                                        n.sub.16 = 1.51633                                                                        ν.sub.16 = 64.15                        r.sub.26 = -42.4824                                                                       d.sub.26 = 73.8203                                                r.sub.27 = 57.4060                                                                        d.sub.27 = 1.0000                                                                        n.sub.17 = 1.80518                                                                        ν.sub.17 = 25.43                        r.sub.28 = 16.3250                                                                        d.sub.28 = 4.5000                                                                        n.sub.18 1.66998                                                                          ν.sub.18 = 39.27                        r.sub.29 = -21.9620                                                           aspherical coefficient                                                        P = -10.0000, E = 0.70425 × 10.sup.-2                                   F = -0.77432 × 10.sup.-4, G = 0.14068 × 10.sup.-8                 L = -0.87328 × 10.sup.-28                                                ##STR25##                                                                    |cos ω.sub.I - cos ω.sub.0.5 | = 0.153          h.sub.1 /I.sub.max = 0.478, f.sub.2 /f = 1.709                                |R.sub.min |/f = 0.427, tan α = 0.3363,               tan ω.sub.1 = 0.833, d/I.sub.max = 4.45                                 ______________________________________                                        Embodiment 28                                                                 f = 4.449, F/5.88, 2ω = 79.6°                                    IH = 1.692, object distance = 50                                              ______________________________________                                        r.sub.1 = 6.3185                                                              (aspherical surface)                                                                      d.sub.1 = 1.0000                                                                         n.sub.1 = 1.78471                                                                         ν.sub.1 = 25.71                         r.sub.2 = 1.9000                                                                          d.sub.2 = 0.9000                                                  r.sub.3 = ∞                                                                         d.sub.3 = 6.7000                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = ∞                                                                         d.sub.4 = 8.2000                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.5 = -7.0109                                                                         d.sub.5 = 2.0000                                                  r.sub.6 = 11.8936                                                                         d.sub.6 = 5.0000                                                                         n.sub.4 = 1.51633                                                                         ν.sub.4 = 64.15                         r.sub.7 = -5.7154                                                                         d.sub.7 = 1.5000                                                                         n.sub.5 = 1.84666                                                                         ν.sub.5 = 23.78                         r.sub.8 = -28.9737                                                                        d.sub.8 = 3.0000                                                  r.sub.9 = 21.4710                                                                         d.sub.9 = 5.0000                                                                         n.sub. 6 = 1.51680                                                                        ν.sub.6 = 64.14                         r.sub.10 = ∞                                                                        d.sub.10 = 13.0000                                                                       n.sub.7 = 1.51680                                                                         ν.sub.7 = 64.14                         r.sub.11 = -98.0103                                                                       d.sub.11 = 44.0004                                                r.sub.12 = 56.2382                                                                        d.sub.12 = 4.5110                                                                        n.sub.8 = 1.51633                                                                         ν.sub.8 = 64.15                         r.sub.13 = -15.4029                                                                       d.sub.13 = 2.0000                                                                        n.sub.9 = 1.74950                                                                         ν.sub.9 = 35.27                         r.sub.14 = -29.6340                                                                       d.sub.14 = 25.6200                                                r.sub.15 = ∞(stop)                                                                  d.sub.15 = 25.6200                                                r.sub.16 = 29.6340                                                                        d.sub.16 = 2.0000                                                                        n.sub.10 = 1.74950                                                                        ν.sub.10 = 35.27                        r.sub.17 = 15.4029                                                                        d.sub.17 = 4.5110                                                                        n.sub.11 = 1.51633                                                                        ν.sub.11 = 64.15                        r.sub.18 = -56.2382                                                                       d.sub.18 = 40.9500                                                r.sub.19 = 51.1534                                                                        d.sub.19 = 22.3000                                                                       n.sub.12 = 1.51680                                                                        ν.sub.12 = 64.14                        r.sub.20 = -51.1534                                                                       d.sub.20 = 40.9500                                                r.sub.21 = 56.2382                                                                        d.sub.21 = 4.5110                                                                        n.sub.13 = 1.51633                                                                        ν.sub.13 = 64.15                        r.sub.22 = -15.4029                                                                       d.sub.22 = 2.0000                                                                        n.sub.14 = 1.74950                                                                        ν.sub.14 = 35.27                        r.sub.23 = -29.6340                                                                       d.sub.23 = 51.2400                                                r.sub.24 = 29.6340                                                                        d.sub.24 = 2.0000                                                                        n.sub.15 = 1.74950                                                                        ν.sub.15 = 35.27                        r.sub.25 = 15.4029                                                                        d.sub.25 = 4.5110                                                                        n.sub.16 = 1.51633                                                                        ν.sub.16 = 64.15                        r.sub.26 = -56.2382                                                                       d.sub.26 = 73.8203                                                r.sub.27 = 57.4060                                                                        d.sub.27 = 1.0000                                                                        n.sub.17 = 1.80518                                                                        ν.sub.17 = 25.43                        r.sub. 28 = 16.3250                                                                       d.sub.28 = 4.5000                                                                        n.sub.18 = 1.66998                                                                        ν.sub.18 = 39.27                        r.sub.29 = -21.9620                                                           aspherical coefficient                                                        P = -10.0000, E = 0.70425 × 10.sup.-2                                   F = -0.77432 × 10.sup.-4, G = 0.14068 × 10.sup.-8                 L = -0.87328 × 10.sup.-28                                                ##STR26##                                                                    |cos ω.sub.I - cos ω.sub.0.5 | = 0.153          h.sub.1 /I.sub.max = 0.477, f.sub.2 /f = 1.709                                |R.sub.min |/f = 0.427, tan α= 0.3345,                tan ω.sub.1 = 0.833, d/I.sub.max = 4.45                                 ______________________________________                                        Embodiment 29                                                                 f = 4.364, F/5.59, 2ω = 80.0°                                    IH = 1.684, object distance =  50                                             ______________________________________                                        r.sub.1 = 5.7934                                                                          d.sub.1 = 1.0000                                                                         n.sub.1 = 1.78471                                                                         ν.sub.1 = 25.71                         r.sub.2 = 1.7137                                                              (aspherical surface)                                                                      d.sub.2 = 1.2000                                                  r.sub.3 = ∞                                                                         d.sub.3 = 6.7000                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = ∞                                                                         d.sub.4 = 8.0000                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.5 = -7.0241                                                                         d.sub.5 = 2.0000                                                  r.sub.6 = 9.4781                                                                          d.sub.6 = 5.0000                                                                         n.sub.4 = 1.51633                                                                         ν.sub.4 = 64.15                         r.sub.7 = -6.0129                                                                         d.sub.7 = 1.5000                                                                         n.sub.5 = 1.84666                                                                         ν.sub.5 = 23.78                         r.sub.8 = -95.6255                                                                        d.sub.8 = 3.0000                                                  r.sub.9 = 28.7313                                                                         d.sub.9 = 5.0000                                                                         n.sub.6 = 1.51633                                                                         ν.sub.6 = 64.15                         r.sub.10 = ∞                                                                        d.sub.10 = 13.0000                                                                       n.sub.7 = 1.51633                                                                         ν.sub.7 = 64.15                         r.sub.11 = -40.9980                                                                       d.sub.11 = 44.0000                                                r.sub.12 = 34.0398                                                                        d.sub.12 = 4.5110                                                                        n.sub.8 = 1.51112                                                                         ν.sub.8 = 60.48                         r.sub.13 = -14.1661                                                                       d.sub.13 = 2.0000                                                                        n.sub.9 = 1.74950                                                                         ν.sub.9 = 35.27                         r.sub.14 = -34.5603                                                                       d.sub.14 = 25.6200                                                r.sub.15 = ∞(stop)                                                                  d.sub.15 = 25.6200                                                r.sub.16 = 34.5603                                                                        d.sub.16 = 2.0000                                                                        n.sub.10 = 1.74950                                                                        ν.sub.10 = 35.27                        r.sub.17 = 14.1661                                                                        d.sub.16 = 4.5110                                                                        n.sub.11 = 1.51112                                                                        ν.sub.11 = 60.48                        r.sub.18 = -34.0398                                                                       d.sub.18 = 40.9500                                                r.sub. 19 = 55.5131                                                                       d.sub.19 = 22.3000                                                                       n.sub.12 = 1.51633                                                                        ν.sub.12 = 64.15                        r.sub.20 = -55.5131                                                                       d.sub.20 = 40.9500                                                r.sub.21 = 34.0398                                                                        d.sub.21 = 4.5110                                                                        n.sub.13 = 1.51112                                                                        ν.sub.13 = 60.48                        r.sub.22 = -14.1661                                                                       d.sub.22 = 2.0000                                                                        n.sub.14 = 1.74950                                                                        ν.sub.14 = 35.27                        r.sub.23 = -34.5603                                                                       d.sub.23 = 51.2400                                                r.sub.24 = 34.5603                                                                        d.sub.24 = 2.0000                                                                        n.sub.15 = 1.74950                                                                        ν.sub.15 = 35.27                        r.sub.25 = 14.1661                                                                        d.sub.25 = 4.5110                                                                        n.sub.16 = 1.51112                                                                        ν.sub.16 = 60.48                        r.sub.26 =  -34.0998                                                                      d.sub.26 = 73.0902                                                r.sub.27 = 57.4060                                                                        d.sub.27 = 1.0000                                                                        n.sub.17 = 1.80518                                                                        ν.sub.17 = 25.43                        r.sub.28 = 16.3250                                                                        d.sub.28 = 4.5000                                                                        n.sub.18 = 1.66998                                                                        ν.sub.18 = 39.27                        r.sub.29 = -21.9620                                                           aspherical coefficient                                                        P = 0.4234, E = -0.20021 × 10.sup.-2                                    F = -0.35366 × 10.sup.-8                                                 ##STR27##                                                                    |cos ω.sub.I - cos ω.sub.0.5 | = 0.089          h.sub.1 /I.sub.max = 0.474, f.sub.2 /f = 1.652                                |R.sub.min |/f = 0.392, d/I.sub.max = 4.58                  ______________________________________                                        Embodiment 30                                                                 f = 4.370, F/5.59, 2ω = 79.9°                                    IH = 1.683, object distance = 50                                              ______________________________________                                        r.sub.1 = 7.0000                                                                          d.sub.1 = 1.0000                                                                         n.sub.1 = 1.78471                                                                         ν.sub.1  = 25.71                        r.sub.2 = 1.8724                                                              (aspherical surface)                                                                      d.sub.2 = 1.2000                                                  r.sub.3 = ∞                                                                         d.sub.3 = 6.7000                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = ∞                                                                         d.sub.4 = 8.0000                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.5 = -7.1300                                                                         d.sub.5 = 2.0000                                                  r.sub.6 = 9.1560                                                                          d.sub.6 = 5.0000                                                                         n.sub.4 = 1.51633                                                                         ν.sub.4 = 64.15                         r.sub.7 = -6.0310                                                                         d.sub.7 = 1.5000                                                                         n.sub.5 = 1.84666                                                                         ν.sub.5 = 23.78                         r.sub.8 = -95.7310                                                                        d.sub.8 = 3.0000                                                  r.sub.9 = 29.4330                                                                         d.sub.9 = 5.0000                                                                         n.sub.6 = 1.51633                                                                         ν.sub.6 = 64.15                         r.sub.10 = ∞                                                                        d.sub.10 = 12.9381                                                                       n.sub.7 = 1.51633                                                                         ν .sub.7 = 64.15                        r.sub.11 = -40.9980                                                                       d.sub.11 = 44.0000                                                r.sub.12 = 31.9122                                                                        d.sub.12 = 4.5110                                                                        n.sub.8 = 1.51602                                                                         ν.sub.8 = 56.80                         r.sub.13 = -13.6341                                                                       d.sub.13 = 2.0000                                                                        n.sub.9 = 1.74950                                                                         ν.sub.9 = 35.27                         r.sub.14 = -35.8745                                                                       d.sub.14 = 25.6200                                                r.sub.15 = ∞(stop)                                                                  d.sub.15 = 25.6200                                                r.sub.16 = 35.8745                                                                        d.sub.16 = 2.0000                                                                        n.sub.10 = 1.74950                                                                        ν.sub.10 = 35.27                        r.sub.17 = 13.6341                                                                        d.sub.16 = 4.5110                                                                        n.sub.11 = 1.51602                                                                        ν.sub.11 = 56.80                        r.sub.18 = -31.9122                                                                       d.sub.18 = 40.9500                                                r.sub.19 = 50.9974                                                                        d.sub.19 = 22.3000                                                                       n.sub.12 = 1.51633                                                                        ν.sub.12 = 64.15                        r.sub.20 = -50.9974                                                                       d.sub.20 = 40.9500                                                r.sub.21 = 31.9122                                                                        d.sub.21 = 4.5110                                                                        n.sub.13 = 1.51602                                                                        ν.sub.13 = 56.80                        r.sub.22 = -13.6341                                                                       d.sub.22 = 2.0000                                                                        n.sub.14 = 1.74950                                                                        ν.sub.14 = 35.27                        r.sub.23 = -35.8745                                                                       d.sub.23 = 51.2400                                                r.sub.24 = 35.8745                                                                        d.sub.24 = 2.0000                                                                        n.sub.15 = 1.74950                                                                        ν.sub.15 = 35.27                        r.sub.25 = 13.6341                                                                        d.sub.25 = 4.5110                                                                        n.sub.16 = 1.51602                                                                        ν.sub.16 = 56.80                        r.sub.26 = -31.9122                                                                       d.sub.26 = 72.9351                                                r.sub.27 = 57.4060                                                                        d.sub.27 = 1.0000                                                                        n.sub.17 = 1.80518                                                                        ν.sub.17 = 25.43                        r.sub.28 = 16.3250                                                                        d.sub.28 = 4.5000                                                                        n.sub.18 = 1.66998                                                                        ν.sub.18 = 39.27                        r.sub.29 = -21.9620                                                           aspherical coefficient                                                        P = 1.0000, E = -0.12829 × 10.sup.-1                                    F = -0.61773 × 10.sup.-2, G = -0.20560 × 10.sup.-7                 ##STR28##                                                                    |cos ω.sub.I - cos ω.sub.0.5 | = 0.080          h.sub.1 /I.sub.max = 0.486, f.sub.2 /f = 1.649                                |R.sub.min |/f = 0.428, d/I.sub.max = 4.60                  ______________________________________                                        Embodiment 31                                                                 f = 4.323, F/5.69, 2ω = 80.0°                                    IH = 1.721, object distance = 50                                              ______________________________________                                        r.sub.1 = 7.0000                                                              (aspherical surface)                                                                      d.sub.1 = 1.0000                                                                         n.sub.1 = 1.78471                                                                         ν.sub.1 = 25.71                         r.sub.2 = 1.8392                                                              (aspherical surface)                                                                      d.sub.2 = 1.2000                                                  r.sub. 3 = ∞                                                                        d.sub.3 = 6.7000                                                                         n.sub.2 = 1.80610                                                                         ν.sub.2 = 40.95                         r.sub.4 = ∞                                                                         d.sub.4 = 8.0000                                                                         n.sub.3 = 1.80610                                                                         ν.sub.3 = 40.95                         r.sub.5 = -7.1300                                                                         d.sub.5 = 2.0000                                                  r.sub.6 = 9.1560                                                                          d.sub.6 = 5.0000                                                                         n.sub.4 = 1.51633                                                                         ν.sub.4 = 64.15                         r.sub.7 = -6.0310                                                                         d.sub.7 = 1.5000                                                                         n.sub.5 = 1.84666                                                                         ν.sub.5 = 23.78                         r.sub.8 = -95.7310                                                                        d.sub.8 = 3.0000                                                  r.sub.9 = 29.4330                                                                         r.sub.9 = 5.0000                                                                         n.sub.6 = 1.51633                                                                         ν.sub.6 = 64.15                         r.sub.10 = ∞                                                                        d.sub.10 = 13.0282                                                                       n.sub.7 = 1.51633                                                                         ν.sub.7 = 64.15                         r.sub.11 = -40.9980                                                                       d.sub.11 =  44.0000                                               r.sub.12 = 37.6000                                                                        d.sub.12 = 4.5110                                                                        n.sub.8 = 1.51009                                                                         ν.sub.8 = 63.46                         r.sub.13 = -14.9830                                                                       d.sub.13 = 2.0000                                                                        n.sub.9 = 1.74950                                                                         ν.sub.9 = 35.27                         r.sub.14 = -33.7510                                                                       d.sub.14 = 25.6200                                                r.sub.15 = ∞(stop)                                                                  d.sub.15 = 25.6200                                                r.sub.16 = 33.7510                                                                        d.sub.16 = 2.0000                                                                        n.sub.10 = 1.74950                                                                        ν.sub.10 = 35.27                        r.sub.17 = 14.9830                                                                        d.sub.17 = 4.5110                                                                        n.sub.11 = 1.51009                                                                        ν.sub.11 = 63.46                        r.sub.18 = -37.6000                                                                       d.sub.18 = 40.9500                                                r.sub.19 = 55.0600                                                                        d.sub.19 = 22.3000                                                                       n.sub.12 = 1.51633                                                                        ν.sub.12 = 64.15                        r.sub.20 = -55.0600                                                                       d.sub.20 = 40.9500                                                r.sub.21 = 37.6000                                                                        d.sub.21 = 4.5110                                                                        n.sub.13 = 1.51009                                                                        ν.sub.13 = 63.46                        r.sub.22 = -14.9830                                                                       d.sub.22 = 2.0000                                                                        n.sub.14 = 1.74950                                                                        ν.sub.14 = 35.27                        r.sub.23 = -33.7510                                                                       d.sub.23 = 51.2400                                                r.sub.24 = 33.7510                                                                        d.sub.24 = 2.0000                                                                        n.sub.15 = 1.74950                                                                        ν.sub.15 = 35.27                        r.sub.25 = 14.9830                                                                        d.sub.25 = 4.5110                                                                        n.sub.16 = 1.51009                                                                        ν.sub.16 = 63.46                        r.sub.26 = -37.6000                                                                       d.sub.26 = 73.0000                                                r.sub.27 = 57.4060                                                                        d.sub.27 = 1.0000                                                                        n.sub.17 = 1.80518                                                                        ν.sub.17 = 25.43                        r.sub.28 = 16.3250                                                                        d.sub.28 = 4.5000                                                                        n.sub.18 = 1.66998                                                                        ν.sub.18 = 39.27                        r.sub.29 = -21.9620                                                           aspherical coefficient                                                        (1st surface)                                                                 P = 1.0000, E = 0.53146 × 10.sup.-2                                     F =  -0.61228 × 10.sup.-4, G = -0.48942 × 10.sup.-9               (2nd surface)                                                                 P = 1.0000, E = 0.61486 × 10.sup.-2                                     F = 0.37818 × 10.sup.-5, G = 0.11647 × 10.sup.-10                  ##STR29##                                                                    |cos ω.sub.I - cos ω.sub.0.5 |= 0.155           h.sub.1 /I.sub.max = 0.496, f.sub.2 /f = 1.667                                |R.sub.min |/f = 0.425, tan α = 0.3563                tan ω.sub.1 = 0.839, d/I.sub.max = 4.58                                 ______________________________________                                    

wherein the reference symbols r₁, r₂, . . . represent radii of curvatureon the surfaces of the respective lens elements, the reference symbolsd₁, d₂, . . . designate thicknesses of the respective lens elements andairspaces reserved therebetween, the reference symbols n₁, n₂, . . .denote refractive indices of the respective lens elements, and thereference symbols ν₁, ν₂, . . . represent Abbe's numbers of therespective lens elements.

The Embodiments 1 through 21 have the compositions illustrated in FIG.22 through FIG. 42 respectively, and each of the Embodiments consists ofa first lens unit I having negative function and a second lens unit IIhaving positive function. Each of the Embodiments is designed as aretrofocus type objective lens system in which an aspherical surface isarranged so the object side surface of a lens element in the first lensunit I having negative function.

Further, the objective lens system has an airspace allowing to arrange afield direction changing prism between the extremely object side surfacehaving positive refractive power in the second lens unit II and theextremely image side surface having negative refractive power in thefirst lens unit I.

The Embodiment 1 has the composition illustrated in FIG. 22 wherein thefirst lens unit I is designed as a cemented doublet and the two lenselements are made of glass materials having different Abbe's numbers forcorrecting chromatic aberration. Further, out of these lens elements,the lens element having the aspherical surface on the object side has aplane surface on the other side. This aspherical lens element can easilybe shaped by molding since it has the plane surface on one side.

The aspherical surface of this lens element serves for reducing negativedistortion and the negative curvature of field produced by this lenselement is cancelled with the positive curvature of field produced bythe object side concave surface arranged on the second lens unit II.Further, the curvature of field produced by this concave surface alsocancels the negative curvature of field to be produced at a later stageby a relay lens system. The Embodiment 1 produces positive curvature offield as illustrated in FIG. 54.

The Embodiment 2 has the composition illustrated in FIG. 23 wherein thefirst lens unit I consists of a single negative meniscus lens element,whereas the second lens unit II consists of two lens elements which areobtained by separating a cemented doublet.

Since endoscopes have thin distal ends, it is undesirable for arrangingfield direction changing prisms to use cemented doublets which thickenlens components. Further, single-element lens components are morepreferable than a cemented doublet since lens shaping and cementingworks become more complicated when a cemented doublet is composed ofthin lens elements.

In the Embodiment 2, the second lens unit II has the same function asthat in the Embodiment 1, but the number of lens surfaces is increasedby separating the cemented doublet and the radius of curvature can beenlarged on the object side concave surface. Accordingly, rays arerefracted by this surface at smaller angles, thereby reducing productionof coma. Further, aggravation due to eccentricity of the lens elementscan be reduced favorably.

The Embodiments 3 through 5 have the compositions illustrated in FIG. 24through FIG. 26 respectively wherein material of the aspherical lenselement arranged in the first lens unit I is different from that in theEmbodiment 2. Further, the aspherical lens elements are different fromone another in the thickness thereof in the Embodiment 3 through 5.

Since shaping conditions such as molding temperature are different forshaping the aspherical lens element not by grinding but by molding, itis possible to lessen hindrance on shaping by properly selectingmaterials. The Embodiment 2 and the Embodiments 3 through 5 are theexamples using the aspherical lens elements made of different materialsand serve for facilitating to select adequate materials for theaspherical lens elements. Further, it is possible to lessen hindrance onmolding caused by the small diameter of the aspherical lens element byincreasing thickness of the aspherical lens element within a rangeallowed by the outside diameter thereof. If outside diameter of theaspherical lens element is reduced while keeping the small outsidediameter unchanged, hindrance on molding will be produced due to toothin edge of the aspherical lens element.

The Embodiment 6 through 10 have the compositions illustrated in FIGS.27 through 31 respectively, and have field angles and/or correctiondegrees of distortion which are different from one another and also fromthose in the Embodiment 1.

Out of these Embodiments, the Embodiments 6 and 7 are designed for afield angle of 70° which is the same as that in the Embodiment 1, anddistortion at degrees of -1.0% and -0.5% respectively in contrast to theother Embodiments designed for distortion at a degree of -4.5%. Theobjective lens systems having distortion at the different degrees makeit possible to observe objects favorably in accordance with shapes ofthe surfaces thereof. Not only objects having plane surfaces but alsoobjects having spherical surfaces having slight irregularities can beobserved as images free from distortion at intermediate image height andmarginal image height by replacing objective lens systems so as toselect an objective lens system matched with shape of an object to beobserved.

Further, the Embodiments 8 through 10 are designed for the same fieldangle of 90° but different in correction degree of distortion. Thesehave a field angle wide enough to permit observing a wide range ofobject without distortion.

The Embodiments 11 and 12 have the compositions illustrated in FIGS. 32and 33 respectively wherein the first lens unit I consists of a singlelens component like that used in the Embodiment 1, but the second lensunit II consists of two lens components both designed as cementeddoublets. As already described with reference to the Embodiment 2, it isdesirable to design both the lens components as cemented doublets solong as coma is not aggravated by the object side concave surface andaberrations are produced at higher degrees. Speaking concretely, thespacing rings are made unnecessary between the lens components and thenumber of component members is reduced by designing the lens componentsas the cemented doublets.

Further, the Embodiment 12 has a total length larger than that of theEmbodiment 11 and permits freely selecting length of the distal end ofendoscopes.

The Embodiment 13 has the composition illustrated in FIG. 34 and isdifferent from the Embodiment 2 in that distortion is -0.5% at themarginal portion of an image formed by the Embodiment 13.

The Embodiment 14 has the composition illustrated in FIG. 35 which issimilar to those of the Embodiments 11 and 12. However, the Embodiment14 is designed for distortion of -10% at the marginal portion of animage.

The Embodiment 15 has the composition illustrated in FIG. 36 and isdifferent from the Embodiment 2 in that the former is designed fordistortion of -10% at the marginal portion of an image. Further, theEmbodiment 15 is designed for curvature of field less than those in theother Embodiments, and permits arranging an image guide and asolid-state image pickup device for application to various purposes.

The Embodiment 16 has the composition illustrated in FIG. 37 and isdifferent from the Embodiment 11 or 12 in that the Embodiment 16 isdesigned for a field angle of 40°.

The Embodiments 17 and 18 have the compositions illustrated in FIGS. 38and 39 respectively. These Embodiments are different from the Embodiment1 in that the aspherical surfaces used in the Embodiments 17 and 18 areexpressed only by the coefficient of fourth order (the Embodiment 17) orsixth order (the Embodiment 18) in the formula for shape of asphericalsurface. It is preferable to design shape of an aspherical surface byselecting only one of the coefficients of fourth order, sixth order,eighth order since such selection simplifies the calculations forexamining shape of the aspherical surface at the design stage,facilitates judgement of the shape, and makes it easy to design andmanufacture molding dies.

The Embodiments 19 and 20 have the compositions illustrated in FIGS. 40and 41 respectively wherein relay lens systems for relaying images threetimes and five times are added in the objective lens systems describedas the Embodiments 1 and 2 respectively.

By adding relay lens systems, as in the cases of the Embodiments 19 and20, for transmitting an image for a selected relay times of 3, 5, 7, 11,. . . , it is possible to obtain endoscopes having required lengths andbrightness. Graded refractive index lenses may be used for composing therelay lens systems to be used in the objective lens systems forendoscopes according to the present invention.

The Embodiment 21 is an optical system having the compositionillustrated in FIG. 42. This Embodiment is an objective lens systemwherein a portion of the long bar-shaped lens component is replaced witha field direction changing prism. By this means, the Embodiment 21 isdesigned as an oblique viewing objective lens system for endoscopes.Further, the Embodiment 21 is an optical system for endoscopes in whichan image is relayed five times by relay lens systems R. In this drawing,the reference symbol E represents an eyepiece, and the reference symbolsC₁ and C₂ designate cover glasses respectively.

In the Embodiments 1 through 20 out of the Embodiments described above,the cover glass C is made of sapphire.

The Embodiments 22 through 32 are examples wherein the objective lenssystem for endoscopes according to the present invention is applied tonon-flexible endoscopes so adapted as to transmit an image formed bysaid objective lens system rearward through relay lens systems and allowto observe the transmitted image through an eyepiece. Each of theobjective lens systems in these Embodiments comprises a first lens unitconsisting of a single lens component having negative refractivefunction and a second lens unit having negative refractive function. Theobject side surface of the single lens component having the negativerefractive function is designed as an aspherical surface in theEmbodiments 22 through 29. Further, the image side surface of saidsingle lens component having the negative refractive function isdesigned as an aspherical surface in the Embodiments 27 and 28, whereasboth the object side surface and the image side surface of said lenscomponents are designed as aspherical surfaces.

Furthermore, each of the Embodiments 22 through 32 comprises, betweenthe first lens unit and the second lens unit, an airspace d satisfyingthe condition (10) and permits arranging such a prism for changing thefield direction as shown in FIGS. 3, 20 or 21. In addition, an image maybe transmitted for an optional relaying times by relay lens systems usedin these Embodiments, and it is possible to obtain non-flexibleendoscopes having required lengths by selecting numbers of relayingtimes.

As is understood from the foregoing description, the objective lenssystem for endoscopes according to the present invention has distortioncorrected sufficiently favorably even at a wide field angle and can formimages of high quality owing to little loss of light quantity at themarginal portion of the image. Further, the objective lens system forendoscopes according to the present invention permits arranging a fielddirection changing optical system therein and can be designed as anobjective lens system usable for allowing observation in variousdirections.

What is claimed is:
 1. An objective lens system for endoscopescomprising, in the recited order from the object side:a first lens unithaving negative refractive power and a second lens unit having positiverefractive power; said lens units being arranged in such a manner that aprincipal ray passes substantially through a front focal point of saidsecond lens unit for making the principal ray emerging from saidobjective lens system substantially parallel to an optical axis of theobjective lens system; said first lens unit including a negative lenscomponent having a concave surface on the image side thereof, bearing asubstantial portion of the negative refractive power of said first lensunit and satisfying the following condition (1), and said objective lenssystem comprising an aspherical surface satisfying the followingcondition (2) at 50% or more of the effective area determined dependingon the maximum image height: ##EQU9## wherein the reference symbol R₁represents radius of curvature on said concave surface, the referencesymbol f designating focal length of the objective lens system as awhole, the reference symbols ω_(I) and ω₀.5 denote field angles at animage height of I and at 1/2 of the maximum image height respectively,and the reference symbols K_(I) and K₀.5 represent values of K at theimage height of I and at 1/2 of the maximum image height respectivelywhen K is defined as K=sin θ₂ /tan θ₁ (the reference symbol θ representsan angle formed between the optical axis and the principal ray incidentfrom the object side on said aspherical surface located on the extremeobject side, and the reference symbol θ designates an angle formedbetween the optical axis and the principal ray immediately afterrefraction by the aspherical surface located on the extreme image side).2. An objective lens system for endoscopes according to claim 1satisfying the following conditions (3), (4) and (5):

    h.sub.1 /I.sub.max ≦2                               (3)

    f≦f.sub.2 ≦10f                               (4)

    |R.sub.min |≦1.5f                 (5)

wherein the reference symbol h₁ represents height, on the extreme objectside surface of said first lens unit, of the principal ray to attain tothe maximum image height, the reference symbol I_(max) designates themaximum height of image formed by said objective lens system, thereference symbol R_(min) denotes the minimum radius of curvature on theconcave surfaces including said image side aspherical surface on thefirst lens unit and the reference symbol f₂ represents focal length ofsaid second lens unit.
 3. An objective lens system for endoscopesaccording to claim 1 wherein said aspherical surface is located on theobject side and said objective lens system is so designed as to satisfythe following condition (6):

    0≦tanαtanω.sub.1                        ( 6)

wherein the reference symbol α represents angle formed between theaspherical surface and a plane perpendicular to the optical axis at theintersection between the principal ray having the maximum image heightand said aspherical surface, and the reference symbol ω₁ designatesfield angle of the objective lens system.
 4. An objective lens systemfor endoscopes according to claim 1, 2 or 3 wherein said asphericalsurface is expressed by the following formula: ##EQU10## wherein thereference symbols x and y represent values of coordinates when theintersection between the optical axis and said aspherical surface istaken as the origin, the optical axis is taken as the x axis, and thestraight line passing through the origin and perpendicular to theoptical axis is taken as the y axis, the reference symbol C designatesan inverse number of the radius of curvature of the circle in contactwith said aspherical surface on the optical axis, and the referencesymbols E, F, G, . . . denote the aspherical surface coefficients of thefourth order, sixth order, eighth order, etc.
 5. An objective lenssystem for endoscopes according to claim 4 wherein said asphericalsurface is designed as a surface located on the image side and at leastone of the aspherical surface coefficients of fourth and higher ordershave a negative value.
 6. An objective lens system for endoscopesaccording to claim 4 wherein said aspherical surface is designed as asurface located on the object side and at least one of the asphericalsurface coefficients of fourth and higher orders have a positive value.7. An objective lens system for endoscopes according to claim 1satisfying the following condition (10):

    2≦d/I.sub.max ≦8                             (10)

wherein the reference symbol d represents distance as measured from thesurface located on the extremely image side out of the surfaces havingrefractive powers in said first lens unit to the surface located on theextremely object side out of the surfaces having refractive powers insaid second lens unit, and the reference symbol I_(max) designates themaximum image height.
 8. An objective lens system for endoscopesaccording to claim 1, 2, or 3 wherein said second lens unit comprises asurface concave on the object side, and optical path length z₁ asmeasured along the optical axis between said surface concave on theimage side in said first lens unit and the extreme object side surfacehaving positive refractive power in the second lens unit satisfies thefollowing condition (7):

    z.sub.1 /f≦1                                        (7)


9. An objective lens system for endoscopes according to claim 8 furthersatisfying the following condition (8):

    z.sub.2 /z.sub.1 ≦0.8                               (8)

wherein the reference symbol z₂ represents optical path length asmeasured between the surface located on the extremely image side out ofthe surfaces having negative refractive powers in the first lens unitand the front focal point of the second lens unit.
 10. An objective lenssystem for endoscopes according to claim 9 further satisfying thefollowing condition (9):

    |f.sub.2 /f.sub.1 |≦8             (9)

wherein the reference symbol f₁ and f₂ represent focal lengths of thefirst lens unit and the second lens unit respectively.
 11. An objectivelens system for endoscopes according to claim 1 wherein a fielddirection changing optical system having reflecting surface for changingthe optical axis of the first lens unit toward the optical axis of thesecond lens unit is arranged between the first lens unit and the secondlens unit.
 12. An objective lens system for endoscopes according toclaim 11 wherein said field direction changing optical system iscomposed of a prism having said reflecting surface, and shape and sizeof the sectional surface of said prism perpendicular to the optical axisare nearly equal to those of the second lens unit.
 13. An objective lenssystem for endoscopes according to claim 12 satisfying the followingcondition:

    1.2<T/D<4

wherein the reference symbol T represents distance as measured along theoptical axis from the object side surface of said field directionchanging prism to the extremely image side surface of the lens componentarranged on the object side in the second lens unit, and the referencesymbol D designates diameter of said field direction changing prism. 14.An objective lens system for endoscopes according to claim 1 wherein acover glass made of sapphire is arranged on the object side of saidfirst lens unit.
 15. An objective lens system for endoscopes accordingto claim 14 wherein said cover glass has a shape of a wedge.
 16. Anobjective lens system for endoscopes according to claim 1 comprising asolid-state image pickup device arranged in such a manner that thelight-receiving surface thereof is located at the position of an imageto be formed by said objective lens system.
 17. An objective lens systemfor endoscopes according to claim 4 wherein said second lens unitcomprises a surface concave on the object side, and optical path lengthz₁ as measured along the optical axis between said surface concave onthe image side in said first lens unit and the extreme object sidesurface having positive refractive power in the second lens unitsatisfies the following condition (7):

    z.sub.1 /f≧1                                        (7).


18. An objective lens system for endoscopes according to claim 5 whereinsaid second lens unit comprises a surface concave on the object side,and optical path length z₁ as measured along the optical axis betweensaid surface concave on the image side in said first lens unit and theextreme object side surface having positive refractive power in thesecond lens unit satisfies the following condition (7):

    z.sub.1 /f≧1                                        (7).